If you use external storage and you have the option, choose eSATA. Basically the same thing as an internal SATA drive as far as speed goes, so it's fast. Get it, the E is for External. Substantially faster than your USB or Firewire drives. For desktop machines you can buy inexpensive expansion cards to add the ports if you don't have them (Shame on you Apple, for not adding them to the new Mac Pro), or use an ExpressCard adapter for the MacBook Pro or similar laptop. Imac and Macbook users are out of luck. Many 3.5" external drives and enclosures are available and tend do cost just a bit more than the USB only ones, but totally worth the upgrade if you're doing any heavy lifting or saving big files.
There are also so-called port multiplier enclosures which allow you to plus 2 or 4 or even 8 hard drives to your computer using one cable (most 8 drive cases use two connections). You can even setup RAID arrays with these drives to act as one giant speedy volume. That's what serious video guys do. This crossing of streams 'could' of course saturate even an SATA connection, as you're trying to throw 4 drives worth of data down the cable designed for 1, though you shouldn't notice that limitation most of the time unless you're editing multiple streets of uncompressed video. Hey, some people do.
The only thing I don't like about eSATA is the damn connectors and cables. In a word, they suck. The cables are not very flexible and worst of all, they fall out all the time because the connectors don't grab each other. It's really surprising to me that this went all the way through the development and engineering stage without someone, or many a whole bunch of people, saying "Hey, maybe we should work on this connector a bit more. It kinda sucks". Is there a trick I'm not getting? As it is, my cables come loose if I touch the drives and they won't mount. Annoying.