A good citrus based de-greaser is best. Don't get anything with toxic chemicals in it. I've never had any problems with a citrus based degreaser, and you could also make you own if you are feeling really ambitious.
A man and his rag: In this video we give you a quick overview of how keep your bike in superb running condition by keeping your drivetrain (i.e. cassette, chain, chain rings, dearailleur) clean....