Many transit agencies are offering free rides with coupon on Dump the Pump Day, Thursday June 21. It's a great day to get to work for free and support local public transportation. If an agency is offering free rides, remember to print out a coupon for each trip you take. Usually transfers are not sold with your free ride, since well it's free.

Southern California:
Foothill Transit free ride with coupon, free tote bag at transit stores
Omnitrans (San Bernardino) free day pass ($4 value)

Orange County Transportation Authority - free day pass valid for June 18-June 22 with Facebook login

List the ones in your neighborhood in this thread.