Western Digital Caviar Green

Because USB2 is the limiting factor in data transfer, the Greens are great in external drive cases. I also have a pair in my multimedia/gaming box for mass storage.

I have those and a WD 640 GB Black for a boot drive filing the lower drive bay in an Antec 900 case. Drive temps have never hit 30 C.
 
Heat and Noise will be important in a exterior enclosure:

These thee drives are all the same size and run at the same temperature. Hard to criticize the choice of any one of them. Compare the stats and pick which one works best for you. I standardized on 7200.12's in my NAS's as they just about match the "green" drives in sound and temps but I like the performance of the non green drives....tho newegg no longer selling them for $79.99

Samsung EcoGreen F2 1TB - 5400 rpm $79.99 @ newegg
WD Caviar Green 1TB - 5400 rpm $85.99
Barracuda 7200.12 1TB - 7200 rpm $89.99