If you're sure the front of the monitor is glass, then a window cleaner like Windex should work wonders.
But, if you're at all unsure whether it is glass, don't use it, or you'll wreck the screen.
A warm damp cloth should work on most screens, and you can buy proper cleaning wipes from certain places.
I remember I got a pack of 100 for about £2, but the place I got them from doesn't stock them any more.
But while they lasted, they were good.