For cables, Monoprice is also a good alternative (and, generally, price-competitive with Amazon).

Another commenter mentioned that Monoprice's HDMI quality has declined; I haven't noticed any problem with their Ethernet and USB cables.

For HDMI, Monoprice goes all the way down to $2: http://www.monoprice.com/Search/Index?keyword=hdmi

Best Buy preys on the 'I need this cable in 30 minutes for the big presentation' customer, and prices accordingly. Try buying coaxial cable - it's obscene!