Scarf Heroine is a free print-and-play skirmish game with a cartoony steampunkish vibe. There are rules, order cards and cute cutout figures, all free for the downloading and printing.
Wolsung is a nice looking set of free wargames rules for skirmishes in a steapunk setting.
James Clay has written a fine article on wargaming in the world of the Difference Engine.
For those who don’t know, The Difference Engine is a novel by William Gibson and Bruce Sterling that takes the reader to a Victorian world in which Charles Babbage’s Difference Engine drives cybernetic steam engines. While I did not enjoy it as much as Gibson’s Neuromancer, it still was a good read.