I've been working on a sequel to Lord of the City for a while now. I'm about 20% of the way through the first draft, but I have the outline roughly worked out and know how the story is going to go. Unlike Lord of the City, the story will be split into 3 parts, and will be told from several perspectives (though Part 1 is from Kenton's perspective - the protagonist from Lord of the City).
No idea when the text will be finished or even ready to send out for feedback to people, but I am hoping to have it completed in 2012. Time will tell.