I picked up my current hard drive at Best Buy for $80 or so (great sale).
I checked Fry's. If you don't mind going with ATA, they have a super-sweet deal right now. 16MB buffer!
Seagate ST3250623A-RK 250GB PATA
# 7200 RPM
# 16 MB Buffer
# Retail kit hard drive
# 5 Year Manufacture Warranty
Price: $ 119.99
After Rebate: $ 69.99
What's good? Seagate, Western Digital. Seagate has the better warranty.
What to look for? Cache size can be a stumbling block. Don't grab one with a 2MB buffer or you're screwed for speed. Spindle speed (5400 are old drives, but they are still out there). NCQ is good.
What's important? Performance, warranty, bang for the $.