I help out at one here in memphis that is based on Boston's bikesnotbombs. I also like the setup they have at bike kitchen in SF. Both those organisations have good websites with pleanty of info.
I really love the coop here (revoloutions, run by Anthony Sircusa). They helped get me on a bike when my previous ride was stolen and I've learned a lot helping out once a week. It's actually a really exciting time here: we just won a substantial United Way grant that will go towards paying several local youths for a 10 hour a week, one year apprenticeship as a wrench. The kids will learn all about bikes, help us service them within the community, and then get build up their own for a multi-state tour next summer.
This is cool because, before, we subsisted in a donated space, with no budget and bikes donated and salvaged from garbage piles. Small donations for bike work has kept us in grease and degreaser and PArk donated a set of tools when the shop was robbed. Now we can maybe buy some tubes, brake cables and 700c wheels and reach more people in the community.
Coops are awesome -- good luck getting yours going.