I've rolled quite a few of my own. If you don't need the USB2 connectivity I'd go for one of
these. I've got both the 400 and 800 versions (which are suspiciously missing from the site...) and they work great. Get a nice Hitachi 5K80 or 7K60 2.5" HD from wherever and you're set. Bus-powered drives are generally more expensive, but you can ease that pain a bit by putting them together yourself.
The only place I know of that has a full-sized bus-powered enclosure is
WiebeTech. If you need bigger storage at the cheaper 3.5" prices, you might want to look at one of those. I've not bought one yet, but it's next on my list.
[edit]: Dammit. I was thinking of
this WiebeTech drive. Doesn't look like it's available as an enclosure. Well shit.