a followup on ebartom's post for kidicalmass (fantastic [and legal] bicycle fun for the family):
http://www.kidicalmass.org/
With locations in:
Chicago, IL
Denver, CO
Eugene, OR (the original!)
Huntington, WV
Portland, OR
Salem, OR
San Diego, CA (via a fb page)
San Luis Obispo, CA
Santa Barbara, CA
Saskatoon SK, Canada
Seattle, WA
Victoria, B.C.
Washington D.C.