I reccomend both Iron Kingdoms and Etherscope- both are quite well done. Dragonmech has some nice ideas in it as well.
However, if you're so inclined, there are some older, non-D20 "steampunk" games that you might like for inspiration, if nothing else.
First would be TSR's Amazing Engine system sourcebook "For Faerie Queen and Country."
The second is the great game, Space: 1889. In some ways, its like RIFTS (bear with me!)- its mechanics aren't the best, but the love & work that went into it are quite evident. Very creative, very "true" to the works of Wells, Verne and others, and it had a number of sourcebooks. There is even a related boardgame, Sky Galleons of Mars.