Armor All just came out with a shampoo for foam canons that's supposed to contain a wetting agent. Otherwise, any highly concentrated car wash will do. The Chemical Guy's stuff are fairly inexpensive for the gallon jugs, and they are very concentrated. Walmart started carrying a good amount of their products lately, and a 1/2 gal bottle of Hondeydew Snowfoam is about $19. Another option might be Meguiar's Hyperwash.