Check www.storagereview.com for info comparing hard drive performance. Seagate's current drives are a good noise/performance combo right now but not silent, and WD caviar's are notorious for their noise levels.
Samsung Spinpoints are the current fav around here - quieter and faster than the seagate (tho I have 4 7200.7's in a RAID -- quiet, but wish I had gotten the spinpoints).
Good point if Samsungs are a possiblity for you, they are generally faster and quieter. Seagate's SATA performance is better though if you go that route, but a bit louder.