Going on hikes via the Sierra Club, leading hikes for the local branch of the Sierra Club, participating on the board of the local neighborhood association, taking classes at the local community college, and joining fundraising half-marathon/marathon walks like Team in Training are good ways to meet people. I have lasting friendships from all those activities (I wasn't looking to date, but the Team in Training-type thing, esp. running and marathoning, is where the boys are).