Lately, I've been searching around for the best deals on the Magnaflow Cat Back exhaust system (part # 15822). Some sites offer free shipping, some offer no sales tax, while others offer both.
PlanetMagnaflow.com owned the all of them. Not only do they offer free shipping and no sales tax, but you can offer a price for the item you are interested in.

I thought it was a gimmick at first, but I gave it a shot anyways. I put in the price that would lock me into buying it and in a matter of seconds I got an email that said "Offer Accepted".

Woot! I walked away with a Magnaflow catback for considerably less than retail.