I might actually vote for Ferrer. I don't think he'd be a good mayor -- he's an old-line county-machine pol -- but the election has already been sold to the main with billions of dollars. And I would like Bloomberg to see that some people in the city still think decent schools and affordable housing are more important than glitzominiums and sports stadiums.
Then, of course, there's Jimmy McMillan, the candidate of the Rent Is Too Damn High party. He's got a sense of humor, and if you're going to focus on one single issue, the increasing unaffordability of housing is a good one. Wouldn't it be great to see this party outpoll the !@#$%ing Libertarians? (Update: Gothamist reports that McMillan has some seriously anti-Semitic, seriously weird stuff on his site. I don't know how they managed to actually read his site that thoroughly; I suppose one could call this obscurity through unusability? Thanks to rubytramp for pointing this out.)
In answer to the obvious question: After their torpedoing of Gore's candidacy in 2000, I will never again vote for a Green candidate under any circumstances, ever. The Green Party's most enduring legacy will be the right-wing Supreme Court we'll have for the next 25 years or so. I'd vote for Bernie Goetz before I'd vote for a Green candidate. (Yes, that Bernie Goetz is running for Public Advocate. Duck!)