Bikes Not Bombs sends refurbished bicycles to Central America for use by teachers and low-income individuals. Check out their website , or call 926-4725. Critical Mass is a monthly bike ride. Although it's a regular event, there is no organization behind it, since there are no officers, leaders, or organized planning. So far as I know, the League of Bicycling Voters , formed circa 1996 to fight the local helmet ordinance, is defunct.
Neighborhood associations have a fair amount of political clout in Austin.
They can make or break proposed bicycle-friendly projects in their area. Most NA's are open to anyone living in the neighborhood, not just landowners. They tend to be run by a small number of enthusiastic people who want their neighborhood to be a nice place. The cores of the groups tend to be pretty small, and they are always glad to hear of someone who wants to contribute. You may not feel like you're changing the world right away, but by working your way into the city's informal power structure, you will be able to contribute significantly in the future.