newegg is a good place to go, they do charge more though b/c of their customer service (which is quite good).
If you're relatively hardcore about it (and that's not that hardcore) you should find the best deal on the size hard drive you want and buy an external case from somewhere like macmall or clubmac.
The lacie someone referenced above me is one of the biggest rip-offs I've ever seen. a 100 gig hd running at 5400 can be purchased for about $50 and the case you can get for an additional $50.
Do yourself a favor and make sure the drive is 7200 rpms.
To find what you want go to http://www.pricewatch.com.
Find the drive you want (or go to bestbuy or stapleseven...sometimes their rebates are REALLY good). Then, go to pricewatch and search "usb hard drive case". You'll find a number of USB 2.0 external drive cases for around $30-$40. you do not need to worry about name brands for those cases b/c they all are normally built off the exact same converter board.
The case will end up being SLIGHTLY larger than the hard drive.
Check out this link for external usb 2.0 cases
2 billion dollars...sir, I'd handle my grandpa's balls for 2 billion dollars.