I just picked up the Western Digital My Book Essential 500GB for about $100. That's the going rate now; I really don't need an external drive but if it's for storage, it's great.

Pro: Doesn't require me to open up the case, screw it in, drag the cables, etc. 101% plug and play. Took it out of the box, plugged it in and I was ready to toss on files

Con: Somewhat slow data transfers but I could live with it.

I'm contemplating cracking it open and just use it as an internal drive but will wait and see how it goes.