A nice homemade concoction for the cleaning fluid is to get something around 50% isopropyl alcohol. Isopropyl alcohol is a nice all purpose cleaner that can also be used to clean your heatsink. You can find 90% pure isopropyl alcohol at a local drugstore, but DO NOT USE it at full strength!! Mix at least 1 part water to 1 part of the alcohol to water it down. This approximately 50% mixture is the recommended cleaning method by Apple! Everyone that we've recommended this to has told us it worked EXCELLENETLY!
Do not use any harsh detergents, especially anything like Windex or any product that contains amonia. Strong cleaning and amonia products can etch the screen surface and can cause the plastic to become cloudy or streaked.
Clean using very, very soft cloths. Some people swear by microfiber polymer cloths (also used to clean camera optics), but others use something as simple as a clean sock (flipped inside out). Usually we recommend you stay away from anything even remotely abbrasive, such as paper towels, or old clothes.
Commercial products DO exist to help clean your screen: you can find LCD cleaning pads at local stores like Fry's, Futureshop, etc.
Some people use "Nice'n'Clean" or "Klear Screen", but the 50/50 water/isopropyl alcohol is usually just as good and cheaper (actually, Klear-Screen and many other cleaners are often just a 40-50% isopropyl alcohol solution).
Never EVER try to peel or scratch off any dried "gunk" from your LCD. Use a cleaning solution... it works, trust us!