My computer's old and it's only got 40gb.

Yes, yes, I know. It's small. Some of you guys probably have a music collection that's larger than that. Maybe even twice as large. Soo...I'm thinking about getting an external hard drive to I can save all the things on my computer I really don't want to lose (music, movies, psp stuff, and family pics) because I think the hard drive might be slowly corrupting. What do I need to look for when buying an external hard drive? I don't one that takes forever to get stuff onto and off of it, but don't really want to pay alot. Any recommendations?