Do you need to be able to carry it different places and plug into other computers? If so, get an external enclosure with eSATA and USB. Some now even have eSATA, USB, and Firewire. eSata is an absolute must for any kind of decent transfer speed.
http://www.thermaltakeusa.com/produc...us/n0012us.asp
If you just want to add extra capacity to your existing computer, take a look at using a mobile rack... you just hotswap in the drive and you're good to go. I love these things:
http://www.kingwin.com/mobileracks.asp
These things are pretty cool, but are USB only:
http://www.tripplite.com/products/pr...productID=3769