The first, and the one I've been using most often recently, is The Artist's Guide to Public Art, by Lynn Basa. If you're interested in finding and getting commissions, I couldn't recommend it more highly. It's full of actually useful information, from where to seek out RFQs and RFPs (don't know what they are? read the book!), to how to write proposals, to what to do after you've won. Contracts, insurance fabricators, it's all in there.
I skimmed the whole book first, because if you're new to the process it'll sound like a lot of gobbledygook (I don't need to know about insurance yet, I'm still looking for proposals to write for, etc). I then went back and used it as a reference when I reached each phase in the proposal process.
Recommended to me by public artist Gregor Turk and also the Fulton County Arts Commission.
Art/Work, by Heather Darcy Bhandari and Jonathan Melber. Another good reference on being a working artist. From how to make an inventory list to how to make a box to ship your work in to issues of resale royalties (which I highly favor. I think the art world is the only industry that thinks artists should not benefit from the increasing value of their work), lots and lots of useful stuff. Slightly weighted from the gallerist's perspective, but noting obscene that I've noticed so far. Numerous quotes from working artists and gallerists, and it has a sense of humor that I appreciate.
The $12 Million Stuffed Shark, by Don Thompson. I haven't gotten very far into this one yet, but it's really interesting so far. The shark in question is, of course, Damien Hirst's The Physical Impossibility of Death in the Mind of Someone Living, which I've seen in person at MOMA and is, as the book cites, like Norman Bates' wrinkly mother floating toward you ready to gum you to death. I heart Hirst. Coming from the commercial-art sector, I'm endlessly fascinated by the complete unreality of fine-art-world economics. I noticed it under the arm of fellow artist Joe Karg and I said, hey I just got that book! And he said, hey it's so good! The end.