Perpetrated Press is in the habit of releasing cross-genre stuff, though.
There is also the d20 Deadlands stuff, steampunk meets Lovecraft and B-movie Westerns. The magic rules are okay, but their Mad Science rules are very nice and have been lifted by a couple of other companies for their games.
Dream Pod 9's d20 Mecha Compendium includes a whole section of fantasy mech, steam included.
In very light doses, Paradigm Concepts "Codex Arcanis" has some small steampunk stuff, mostly guns and the legends of how the nation of Althera used to float in the sky.
For design ideas, Dragon #277 had a steampunk article.
Iron Kingdoms looks good, for what little there is. The company has promised a setting book for more than 2 years now - still not delivered. At least there is a monster book and "character primer" that was both released last year ... finally.