Ticketing venues as another place to work with...

"We recently used Brown Paper Tickets -- see http://www.brownpapertickets.com with much success. You can do different price points and print out sales reports, and elect to receive status reports in your email. Their service fees are also very low (and you can choose to have your guests pay them or to pay them yourself), you can customize your event page with your text and logo, and they donate at least 5% of profits to community-based nonprofits." (this is possibly another avenue: ticketing point -- after buying ticket, directed to carpool site)