I agree.
Scouting
4-H
athletics (specific homeschool PE class, gymnastics for homeschoolers and regular classes, my health club had group fitness classes in the afternoon for kids after school, swim team)
Library programs (if your library doesn't offer programming for homeschoolers, ask them to start, if they provide quality programming at various levels for free, they will come)
Parks and Recreation programs---if they have nothing for homeschoolers again just ask. Gather a few other homeschooling parents and develop what you would like for them to program.
Join a yahoo group for your area. Ours has a group where each member will set up activities and you sign up for what you want to do. So if one parent has kids who love astronomy they set up something at the museum at a group rate or make arrangements with a local astronomy club for a night under the stars and you contact the person (pay any fees to that person) and attend...but you only do the things you want to. That goes for theater performances or park meet ups or whatever.
