When it comes to digital photography many people will spend thousands of dollars to acquire just the right piece of gear. The right camera, the right lens, that last bit of something that they think will take their images to the next level. Ignoring the fact that your camera is rarely the limiting factor in anything, these same people often forget the one piece of equipment that is arguably even more important, their computer monitor. Think about it, once you get home with the pictures you've taken, you copy them over to your computer and then start making decisions. Exposure, contrast, color, you know, all the important stuff that determines what your images will look like in their final form. Unfortunately, most people view their monitor as an afterthought even though they'll spend far more time with their photographs in front of their computer than they did with a camera in their hand. It's the modern day darkroom and should be treated with the same commiserate reverence. So where do we start?
Modern day monitors are LCD
Let's get a few things straight. Nowadays everyone is using LCD monitors. I'm sure if you go searching around the internet you'll find some article written in 2002 by some guy in a basement who refuses to give up his Sony Artisan CRT (in fact here's one now), but that time has come to a close. Even within the field of LCDs, there are a number of factors to consider.
The first thing people notice about a monitor is its size and resolution. If you're serious about photography, don't bother with anything under 24" (or maybe 22" if it's that fancy Eizo 221) at 1920x1080 resolution. Personally, I find even that size cramped and would recommend a 27" at 2560x1400 or a 30" at 2560x1600. More pixels means that you get to see more of your images in your library or more of the image you're currently working on in Photoshop. Plus, who doesn't want more room for palettes. Some people are fans of dual monitor setup, with either their library grid or palettes on the second screen, but I find the break between the two distracting. I'd much rather have a single larger display than two smaller ones, but that is a matter of personal preference.
Unfortunately for you, not all monitors of the same size and resolution are created equal. There are two main types of LCD, TN (Twisted Nematic) and IPS (In-Plane Switching). They're two different technologies to control the color of the pixels in the display. I won't go into the guts of the differences here (that's what wikipedia is for). What you need to take away are these two basic rules: TN = bad for photography, IPS = good for photography.
Now there are certainly exceptions to this, but as this is a primer and not a book, just trust me on this. IPS displays are far less washed out when you're looking at the screen from an angle, they also tend to be more true and accurate when it comes to color reproduction. They also tend to use IPS panels in displays with better backlighting and fancy calibration tools. So if you're serious about this stuff, invest in an a good IPS display. IPS panels also tend to have much larger color gamut (that is, they can display a larger range of colors). Some even come close to covering the whole AdobeRGB color space, which is pretty huge.
This is probably a good time to point out that almost all laptop screens up until recently were TN panels. Both because they were cheaper and because they don't require as bright or power hungry backlight. Exceptions to this are the new Apple Retina Macbook Pros, the Thinkpad x220, and a few Acer models that I've seen. This is all to say that if you've only ever edited your pictures on a 4 year old white Macbook with an unprofiled screen, then you really have no idea what your pictures actually look like. Imagine trying to color correct while wearing rose-colored sunglasses. Speaking of calibration...
Calibration and Profiling
Whatever monitor you end up getting, it will likely not be very accurate out of the box. At the very least get yourself one of those puck kits like a Color Munki or i1 Display Pro. Here's how they work: The software displays a series of color patches on the screen while the colorimeter or 'puck' sits on the screen and measures the color. Since the computer now knows both what color was supposed to display and what color DID display, it can create a curve to compensate for the error. It creates what's called an ICC profile which is just a file that the operating system uses to translate and ensure that what the computer is asking for gets shown on the screen accurately. This is the bare minimum when it comes to color accuracy.
The next step up are monitors with what are called Internal LUTs which stands for Look Up Tables. Basically it does a similar translation as the ICC profiles, but it does it in the monitor itself at a much higher degree of accuracy and independent of the computer it's connected to. All of this is a good thing. Monitors with internal LUTs tend to be much more expensive, heavy, and geared toward pros, but man are they worth it if you can afford it.
Part of the problem with buying an expensive monitor is the worry that what you buy will be obsolete within a year or two. Good LCDs have been consistant for the past few years, the latest models just minor upgrades from the previous, but there are some things on the horizon.
Top level screens still tend to use CFL backlights, that is, old-school florescent bulbs. Many cheaper screens now use LED backlights which tend to be more consistant over their life-time, use a lot less power, lead to thinner screens, and turn on almost instantaneously as there is no warm up period. For some reason however the high-end screens still use CFL. I'm sure there's a good technical reason relating to color gamut, but keep an eye out for that.
Update 1/7/14: A number of high-end screens have started to be released with LED backlights. The new NEC PA302W for instance has a tricolor LED backlight system which still allows for wide color gamut.
Another thing that's coming down the line is 10bit per channel color. More bits means less dithering between colors in gradients and such. Some screens can do this today via displayport, but only a few high-end workstation video cards will output 10bit, and as far as I have found in my research, only on Windows at the moment. Personally I'd love to have it, but I'm not going to spend $1000 on a workstation graphics card that's slower than a $200 gaming card just to get it. They should really enable 10bit color channels on all video cards at this point.
Then there is resolution. 30" displays have been at 2560x1600 since the Apple 30" Cinema Display came out in 2004. With all this High-DPI 'retina' screen talk on mobile and laptop devices, it's only a matter of time until desktop screens fly up to higher resolution. 4096px or 4k most likely. Whether this will happen in the next year or two is anyone's guess. I have heard that making panels at 30" with that many pixels is still really difficult. The manufacturers are getting very low yields (the percentage of screens that are defect free) at the moment. But again, only a matter of time.
Update 1/7/14: Hallelujah! The 4K revolution has begun! A couple of months after I originally wrote this post, Asus came out with a 32" LED backlit display with a 3840 x 2160 resolution. It cost $3500 and the color accuracy wasn't great, but it was a first step. Then in last December, Dell started shipping it's own 32" 4K for $3500 as well as a 24" version for $1300. Both were part of Dell's PremierColor line which means they come calibrated from the factory to have a Delta-E of less than 2. Pretty good straight out of the box. I bought one of these 24 Dell UP2414Q displays and have used it to replace my aging NEC 3090, though not without some trouble. Getting this may pixels from your computer to the display is still a little bit of a black art and not for the faintest of hearts. I'm sure all the kinks will be out in the next few months. In the meantime this is on the cutting edge, so be prepared to cut yourself.
So let's say that you've been listening all this time and are interesting in upping your game. Here are a few recommendations. One thing to keep in mind is that while there are screens from 50 different manufacturers, the actual panels inside them are only made by a handful of companies. LG and Samsung alone hold over half of the total LCD panel marketshare. The differences between manufacturers and models are in the backlight systems, input circuitry, etc. Imagine the same engine in a VW Jetta and an Audi A4 Quattro. Same motor, very different car.
If you have a decent screen and can't spend any money at all, but find that the prints coming out of your printer are way too dark, then your screen's brightness is too high. Pull that brightness down and you'll be more accurate, save yourself some money on electricity, and save your eyesight.
If you've got a decent screen and are not getting great results out of the box, buy yourself a colorimeter kit and profile that puppy up. This is bare minimum if you're serious about seeing your images as they actually are. I'm personally a fan of the xRite products like these:
If you're coming from nothing and want to spend less than $1000, get yourself a quality IPS screen and a decent profile system. A lot of people really like the Dell Ultrasharp series of monitors. The main problem with Dell monitors seems to be that they're WAY too bright when they come from the factory, but once you pull the brightness down they tune right up. These links are from Amazon, but keep an eye out for big sales at Dell.com. Be sure to profile with a colorimeter like the the ones listed above.
Some Cupertino diehards are going to demand an Apple Display. That's too bad, because while they're very pretty, they're overpriced for the performance they deliver. Same panel as the Dell above for almost twice the cost, and that's before Dell's frequent sales. Also, many people dislike glossy displays. While blacks can tend to look more black and things are arguably a bit sharper, reflections can be a really serious problem and make it difficult at times to judge what's really there on the screen. Again, be sure to profile with a colorimeter like the the ones listed above.
If you're really serious and want to buy the monitor that'll last you for years there are really only two choices. NEC or Eizo. Eizo are more expensive and cooler looking, but quality for quality they're both in the same ballpark. These three monitors include their own calibration systems.
And if you want to play with fire, you could try one of the new generation of 4K displays. Remember that you'll need a graphics adapter with DisplayPort 1.2 and it software support is still a bit spotty. For instance, Mac OS 10.9.1 doesn't yet allow for MST mode which gives you 60Hz refresh rate at it's highest resolution, and you need to run a terminal command to enable HiDPI mode. Again, be warned, but the images and text do look just lovely.
Now some people will say, "What? You must be out of your damn mind if you think I'm going to spend $1000+ on my monitor!" Well that's just fine, but think about how much you've spent on your camera? How about lenses? Or your computer? My $2000 30" NEC that I bought 5 years ago saw the coming and going of 4 camera bodies which cost about $12,000. Think of it as an investment in a great pair of glasses that let you read accurately and without strain. I've never heard of someone having buyers remorse after upgrading their screen.