Correction to the drives I am looking at:

Samsung Spinpoint T Series HD401LJ 400GB, 7,200 RPM
Western Digital Caviar SE16 WD5000KS 500GB, 7,200 RPM

Notice the Samsung is now a HD401LJ, not a 400. Difference is 16MB vs 8MB cache buffer. 401 just came out in November. I'm leaning towards that one at this point. Now I'm looking for a good enclosure for it that supports ESata and USB. Don't need firewire.