I helped work on GURPS Steampunk, so I am a bit biased when I say that I really enjoy that game. I found it quite easy to use it to run a Holmesian-Steampunk game that friends talked about for a long time.
Forgotten Futures, by Marcus Rowland, is probably the source for Victorian era gaming information and steampunk adventures. Each volume is based on material written from that era, and they are included as text files, so you can really get a good idea of what things were like then. I can highly recommend this.
Space: 1899, for all the clunkiness of the system, has some great background and is worth finding. That can be tricky, but worth the effort.
I know that Battlefield Press is coming out with a couple of Steampunk-feeling games. One will be called Gaslight. It mixes elements of Victorian fiction together into a world of mystery, magic, and science. I wish I could tell you more about it, but NDAs restrict me. Let's just say that my gaming group saw this and immediately wanted to know when we were playing.