How about those CD scratch remover thingies? (just kidding).
Actually, to clean my glasses/sunglasses, I use the cloth towels ($10 for a box of 100) and the eyeglass cleaner solution, both available form Lens Crafters. *Since they are formulated to be easy on delicate plastic lenses with scratch-prone anti-glare covering, they are definitely easy on the guitar finish too, so I just use them on my guitars as well. *I usually reuse each cloth 4 to 10 times and get a new one when the cloth starts leaving its own streaks of gunk, just as I do for glasses. *I just spray a little cleaner on the guitar or on the cloth and wipe it down with the cloth. *
It is important to use cotton cloths like these ones, since paper towels or anything *else with paper in them will scratch the plastic lenses, and will also probably scratch your shiny pickguard.