Dont use anything that has ammonia in it such as 409 or Windex. Potentially it could streak the screen coating (permanently), but I'm guessing most screens today have been tested against ammonia cleaners, its not a good idea anyway.
This link is for the cleaner the Newton users used. It is supposed to recondition the screen.
I use the Read-Right one-step CRT Terminal Cleaning Pads, but they still leave some streaks, so I usually use some Windex, albeit "sparingly" to take the streaks away.