[Compusmurf]

I use a professional photo lens cleaning solution called ROR and a cleaning cloth designed for lens cleaning. It really cuts off the oil from fingers, pollutants in the air, etc. Of course, if you're not a photographer with lots of lenses that you change then this many not be the easiest/cheapest route.

Whatever you choose to use (windex, etc) do NOT use a paper towel. Paper is made from wood fibers and other not necessarily desirable recycled substances. It can cause micro-scratches on the screen. (This goes for LCD TV's, computer screens, and any other device with a soft plastic based screens)