What I do is I take the specifications that my board can handle, and search for the hard disk with those characteristics.
Like, if your board has SATA2, add SATA2 to your search parameters. If you want a 7200rpm drive (and believe me you do if you like performance), add that. If you want a certain size cache, like 16MB, add that too. Which is the hard disk I was searching for.
Ultimately, I didn't care about noise, or HDD size (since most are over 100GB these days at cheap prices). I just cared about price (under $100), and that it had 16MB cache, 7200rpm, and SATA2. And I came up with the WD2500KS for $60.
Western Digital drive 250GB, 16MB cache, 7200RPM spindle speed, Sata 3Gb/s. Frankly it's the best hard drive I could have asked for, except I really wanted a 10000RPM drive for really good performance, but the only one I could find was SATA1.
If you don't care about SATA2, the following are good hard disks to choose from:
HDIUSDSATA14016 (Ascend Tech, 140GB, 7200RPM, 16MB) $48
6L200M0 (Maxtor, 200GB, 16MB) $59
If you wanna play video games, I HIGHLY suggest you buy a hard disk with the following: 7200RPM or higher spindle speed. and 8MB or higher cache. It dramatically reduces loading times.
I remember at a LAN party I was playing RA2 with some friends, and it showed the loading progress of all your friends on the screen in a LAN game. My friend had a new computer he built himself, but sadly didn't know anything about HDD specs, so I assume he had a 5400RPM. Mine was 7200RPM and loaded so much faster and he couldn't help but ask "how you do that?" hehe