Western Digital has a great line of external drives (http://westerndigital.com/en/products/index.asp?cat=5) -- from the one terabyte (yes, 1000gig), to pocket sized 20 or 30GB drives. Their "MyBook" line is designed to look kind of like books, so you can stand them neatly on a shelf and not have it looking like a clunky hard drive.

Also, check the PC/laptop you'll be connecting it to for USB 2.0 ports. While all USB 2.0 is backwards compatible with USB 1.1, having the 2.0 will make it much much faster to transfer files.