I use a clean wash cloth moistened with distilled water (that way minerals in the water won't discolor the screen over years of cleaning). Oh, and it is good to turn the laptop off, as most of these LCD screens are slightly pourous. Dry it off with a dry cloth. Wait until all of the wet spots on the screen dry before turning it back on.
OR, you can go spend 19.95 for a "laptop screen cleaning kit" (yes, I have seen such a thing).
Nack