I could give you quite a few recommendations, but first I need to know what you're using the drive for. There are numerous options out there as well as building your own, but in order to recommend the "best" I need to know what it's use would be. I've used USB, firewire, firewire-800, and eSATA from about every manufacturer out there. Each have their uses as well as pros/cons.
USB -> WD makes a pretty solid unit. I actually have 3 of them.
Firewire/Combo -> LaCie makes some pretty solid units as well, but they cost more than some of the other models out there.
eSATA -> My current favorite is a unit from Sans Digital. It's a TowerRaid Unit supporting up to 4 drives. I've got 2 1TB drives mirrored in it for working on some of the large projects I deal with. It's pretty bulletproof and a lot faster than any USB or Firewire drive setup you'll find. It's also the most expensive.