I always used Windex until I found out about Mr. Clean Magic Erasers. They are the BEST thing I have ever found to clean computer cases, keyboards, everything. Just don't use them on any decals or painted logos. Most of the time they will be okay, but there are certain types of paint used in logos, etc. that didn't bond well to the plastic and can be rubbed off with these Magic Erasers.
An even better thing to do (which will get it looking like new) is to take the computer apart (if you are technically inclined) so all you have is the plastic shell. Put that in the dish washer. It will come out looking like it has newly arrived from the factory. It's amazing really.
In fact, you can put circuit boards in a dishwasher and it will clean them without harming them. Just make sure they are completely dry (like for a week) before using them again.
