If reliability is your #1 concern, then the Western Digital Red drives are probably hard to beat at the price. I just bought 3x 2TB Seagate Barracudas (7.12) for a NAS. They are fast (almost performing on par with the Caviar Blacks) and cheap but there have been a lot of reliability complaints. I'm hoping the latest firmware will help in this area, but it's too early to tell.
For a desktop environment, the slower spindle speed of the Caviar Reds may not be optimal. But probably unbeatable for reliability at the price. However, they're still too new to really judge real world reliability. If you want a reliable, fast desktop drive you really need to shell out for something like the Caviar Black or an enterprise grade drive which are even more expensive.
Unfortunately there doesn't seem to be a lot of good options these days for affordable yet reliable mechanical drives. I would take whatever drive is cheapest that comes with a minimum of 3 year warranty and make sure that I had recent backups of anything important I stored on the thing.
If forced to make a recommendation, I'd probably say go with the to 2TB Hitachi
linked above. It is 7200 RPM and comes with a 3 year warranty. Either that or a Caviar Red.