I've tried a few different cleaners that have been mentioned here, but the one that I found gives the best, longest lasting shine on the SM's black cases is Motul Shine and GO. It ;s silicone based, but the nice thing is that if you overspray onto any other bike part, it wipes away without streaking. I also use it on the front forks and wheels. The bugs and brake dust are easier to clean off.
It's great stuff, smells nice, and is only about $8 a can.
