Audio concepts mobile is good if you really want to drop ALOT of money on your stereo. My buddy Matt works at the A&B by sunridge mall, he does really good work, and i am guessing its gonna be cheaper (my assumption).
I don't know if you are looking to get a deal on the unit/install, but any audio installer should be able to do the work pretty seamlessly.
As for a deal on the unit, try ebay stores, i have had good experiences. Just need to make sure that the installer will put in equipment purchased elsewhere.