Be wary of some decks that have iPod/iPhone integration features like displaying song info on the deck's screen if you have a large number of songs on your iPod. I've tried plugging my 7000 song iPhone into some of these decks and had to wait an excruciating amount of time for it to scan the song library. I'd try any deck with this feature out on a large library to make sure.

Me, I still use a cassette adapter (Sony's sound best to me) and a Pro Clip dock to hold the iPhone.