This is really old news, but Craigslist confirmed that it will be charging for apartment rentals in New York. This adds a second category, the other being jobs, to its source of revenues. I believe that Peter Zollman's Classified Intelligence has estimated annual Craigslist revenues at $10 million (that's my memory).
A long time ago now (about a year and a half ago), I was on a panel with Craig Newmark at Real Estate Connect, a vertical trade show produced by Brad Inman (founder of HomeGain and now TurnHere.com). I think he alluded then to considering the move, as much to deter spam and other unethical practices as to make money.
The remarkable thing about Craigslist (among many things) is its "restraint." As I've said to many people … If Craigslist had VC money when it started it would not exist today. Slow and steady wins the race.