Standard Windex contains ammonia and is absolutely NOT suitable for cleaning LCD screens. Once shouldn't kill it, but repeated applications introduce a slight cloudiness to the surface. Haven't you guys seen the results?
Windex makes a different formulation for plastics: Windex Electronics. Alternatively, a solution of ordinary hand dishwashing liquid should be ammonia-free and is considerably cheaper than Windex.
Dell advocates a standard 50% isopropyl alcohol solution - definitely NOT ethyl alcohol, acetic acid, etc.
I advocate distilled water on a microfiber cloth. I use a slightly coarser type of microfiber meant for car duco; it's like a tiny brush and removes everything I've had to deal with.
It goes without saying that you shouldn't spray anything directly onto the screen.