The best tome in regards to relative and comprehensive "steampunkedness" themes, is the Mongoose Publishing masterpiece, OGL Steampunk. It's a wonderfully detailed tome, combining both old and new material in one easy to access sourcebook. It also introduces a generic steampunk setting that can be used as a template for home campaigns.
As well as this, there are also significant new campaign and character creation elements which really incorporate the feel of 18-19th century European society in a standard D&D campaign.
I suggest you also look into this tome, if you're really serious about this idea.
I've found the Iron Kingdoms setting fairly good for a notion of an Industrial Fantasy society.
I'd look at that and the new Masque of the Red Death.
Both settings definitely provide the steampunk fan with incredible options for his/her campaigns. Although, if you're looking for a strictly Earth-themed interpretation of the "steampunk" era, Masque of the Red Death is by far the best option. It also provides some interesting cultural information for the pre- and post- Industrial periods of Europe.
The setting portrayed in Iron Kingdoms is more in line with bringing "steam-powered" technology into greater emphasis than was actually present in our own history.