best buy is circuit city colored blue and yellow. there is zero discernible difference.
i think crutchfield online has a better track record for customer service and their DIY guides are usually pretty thorough and well-done.
for brick&mortar, either independent shops with good reps or out here we have a chain of higher-end audio/video stores named Tweeter, Etc. they tend to be a bit better than the highschoolers at BB and CC, but you still have to be careful.