I've used some of the products mentioned here (such as AquaWax and 156) and they are really good. A very similar product that is inexpensive and can be found locally at most auto stores and even at WalMart, is Lucas Slick Mist Speed Wax. Lucas is as versatile as AquaWax in that it can be used on all car surfaces, either as a drying aid or as a "topper" on a dry, clean car.
I buy mine at WalMart and Slick Mist there is even slightly cheaper than AquaWax so it really represents an outstanding value. It is not talked about very much but this is an excellent product due to its performance, versatility, availability and price point. The great "bubble gum" smell is a nice bonus.