The Imperial Age: London is one of the best little supplements I have seen out there in a time. At least to my taste. Built around a historical Victorian London guide, which adds to the feeling of credibility it then expands. In ends up detailing too the basics of Victorian society, the government, the workhouse system and even how you are supposed to behave in a club.
This is about the real London, not a steampunked version of it, but even steampunk lovers can make use of it. If you are into XIX century roleplaying, you can't go wrong with this one for 13 bucks!
[4 of 5 Stars!]