Western Digital or Seagate is a good choice... newegg has a 500GB sata-300 (with 16MB of cache memory) for $80 + postage. Newegg.com - Open Box: Western Digital Caviar SE16 WD5000KS 500GB 7200 RPM 16MB Cache SATA-300 Hard Drive (+ tax? i don't know how its worked out in america or if its included in the price)
personally i only ever buy Seagate drives, and, with Seagate taking over Maxtor & just rebadging their own drives with the Maxtor name, and Seagate also offer a 5 year warranty on both Seagate & Maxtor drives, so, now i will only buy Seagate & Maxtor drives
don't be fooled by SATA 300 or SATA 2/II, because the real performance benefits are not seen yet, as hard drives barely reach 130MB transfer rate, never mind the SATA 1 standard of 150, but then again, most drives are SATA 2 compliant anyway...
SATA2 does have a advantage over SATA1 if the data you want is already in the disks cache memory (which is considerably faster than the magnetic disk).