Autism Speaks an advocacy org for Autism holds a number of rides around the country to raise funds.
I rode in last Fall's ride in Chicago ( former co-worker of mine has an autistic son) and it was an amazing experience. There must must have been over 1000 riders. We stretched for over a mile in a double line. It was incredible.
They have rides in Chicago, Colorado, Philadelphia, Southern California, and Las Vegas.
The ride costs $30 and the funds go to a good cause and good organization.
The ride website is
http://www.autismspeaks.org/ridenow