Rod Lee showed me this stuff when we went Kokanee fishing at Berryessa. It worked great!

http://www.tacklewarehouse.com/Peregrine_250_Eagle_Eye_Screen_Cleaner/descpage-PEESC.html

Tackle Tour reviewed the Wave Away screen cleaner and seemed to like it.

http://www.tackletour.com/reviewwaveaway.html

Eye cleaner works great too as Lake said. Costco has their Kirkland brand that comes with two spray bottles and a couple microfiber towels. When you run out of eye cleaner, there's a dispenser of eye cleaner that they have there. As long as you have the spray bottle you purchased originally, you can go there and get refills free of charge.