macally NSA2-S350U Aluminum 3.5" USB 2.0 External Enclosure
http://www.newegg.com/Product/...x?Item=N82E16817347021
$40 +shipping
It's out of stock right now, but that's the one I have. I actually have two of them. They work exactly as any other external enclosure, only with two drives instead of one. I use Seagate 1.5TB drives all-round, so I have 6TB across two of these enclosures.
PRO:
Relatively cheap
Fan cooled with vents
Two drives
Looks pretty sharp IMO
Uses power brick instead of wall wart
Very compact
CON:
Fan is temperature controlled and while normally a good thing, tends to spin up-and down-and up-and down if the drives get warm
If both drives are accessed at once, performance seems to go down a bit per drive (but I think this is true for any dual drive enclosure - I've had two others)
Shipped with jumper set to span drives so both drives used same drive letter, yet wasn't in RAID (I didn't want this, and manual wasn't clear on jumper setting)
I own two because I liked the first one enough, after I jumpered it to my liking, that I purchased a second.