Tire Wet (the good smelling stuff, as mentioned) is made by Black Magic. Any thing I use has been mentioned already I think, including Zep from a dealership.
To whoever was saying to spray truck bedliner, are you talking about on your tires on on the wheel well? If you're spraying truck bedliner (rubberized undercoating) on a wheel well, you want to make sure you let it dry for a LONG time, put fans on it and all before spraying with this, otherwise it will trap in water and create a rust formation. If you're spraying it directly onto your tires, I guess that'* the craziest thing I've ever heard of using but here'* to ya if it works.
Just my .02.