Search moddiction, raxiom, rosen, sintegrate - same head unit with slightly different flavors of operating system. Lots and lots of discussion. Moddiction is probably the best choice based on the price and the "Sync 3 look" interface.
I have the Sintegrate unit myself. Great piece for the price, only downside is the quality of the screen and occasional system crashes. It's too dim during the daytime.