Just dab some water on the inside of a thermal lense, particularly for Vforce, Dye and Raven goggles. They all have an anti-fog coating that you can wash off with cleaners (goggle cleaner, windex, alcohol mix) or rub off by buffing too hard. (found that out the hard way and crapped up a set of Dye lenses)
For the outside, plain old H2O works fine. I use a 50/50 water/alcohol mix but it can affect the lense over time. The snorkeling stuff would probably be fine but water is free and I'm a cheapskate.