I just placed my first car stereo order at cardomain this month, and I'm happy with the purchase. They're serious about their 105% price guarantee: If you e-mail them a link to a lower price for an item on an authorized reseller's site, they'll send you a coupon code to make up the difference. (although my savings got offset by losing the free wire harness and discounted antenna adaptor...)
Also, I found an open-box deal on a Kenwood iPod integration unit there, at $25 instead of the list price of $99. It works great!
Crutchfield does occasionally run some sales, on thanksgiving weekend they had everything discounted.