I know about 800.com and mobshop (which doesn't seem to sell recievers right now, but what other stores sell this hardware and have coupons available?

Amazon has basic receivers and while they don't have coupons right now, a little bit of effort at a few sites (freeride, firstlook, etc) will provide GCs.

Speaking of Amazon, they often have great deals on their closeouts; e.g. a few weeks ago they had the Denon 5700 for about $1400 (nearly 50% off).