Only way to go is get an IPOD supported deck and run it hardwired. Cable itself is like $35 and is an optical line, my IPOD has all of it's buttons on my 7'' screen, and there is no lag, instantaneous response and I never have to see it. I would rather have 8,000 songs unseen than 8,000 songs on disk in my car lol. I have mine wired through the dash and the IPOD itself is in the glove box unseen. The cool part is my computer is set for 380kbps at 48khg sample rate... highest quality i could get, much better than your standard mp3. Quality is near CD but not quite. Also I have 20gb of movies I can play at a touch of the screen, so no storing movies in the car too.. probably the best upgrade i did.
Whatever you pick make sure it has the same IPOD type bottom connector because it's what all the cables fit. Some manufacturer offer "universal" USB type inputs which are better than the crappy circuit city speaker jack will provide but no where the versatility of the hardwired route. Problem with that is the screen will run $700-2000 but they are pretty powerful.