Fry's Electronics, OfficeMax, Office Depot, Staples, or Best Buy
because of their 100% money back guarantees (I don't know about Circuit
City's policy, which recently changed), unlike CompUSA, which charges
15% on opened packages (sometimes whether they were really opened or
not). Fry's is often the cheapest, after rebate, but either Staples or
OfficeMax occasionally offer a drive for a really low prices without a
rebate.
Seagates offer the longest standard warranties, 5 years for internal
desktop drives, and they're about the quietest, and their hottest chips
don't seem to get as hot as those in some other brands (I don't know
about Western Digitals because their chips are on the inner side of
the circuit board).