shudder Craigslist.
I'm older and have had a super hard time finding anyone that's been down for it, and have tried virtually everything (OKC, PoF, Match, and a bunch of the sketchier sites.) Even though I've only been successful once this year, nothing compares to the volume on Craigslist. I've also be shocked (in a good way) at the quality of some of the women I met IRL from CL.
If you're a woman, it's shooting fish in a barrel. If you're a guy, there is real work involved. I kept close track of my stats to see what works and what doesn't, and you can realistically expect to run 50-100 ads before meeting one woman, and you'll have to meet 3-4 women before you'll bed one -- and you may have to see her more than once for that to happen.