You could use any eyeglass cleaning cloth available at any pharmacy. Although you could use just a regular cloth (e.g. shirt), I still recommend the microfiber eyeglass clothes. Ask anyone that uses eyeglasses made from glass (like me). Even optical glass can scratch, although it is much much more difficult to scratch than any plastic. Just play it safe and get microfiber cleaning clothes. I keep one at my house, in my office and in my car... plus I usually take one with me.
Also, the microfiber clothes actually do a much better job of cleaning the screen. Dirt, oils and smudges wipe away with ease with a microfiber cloth, whereas a regular cloth doesn't do an effective job. If you want to save money, some auto supply stores sell fine microfiber chamois that you can cut up into smaller pieces. Just get the ones without piles.