Does your dealership use Groupon?  Groupon can be used from your service department to pre-owned vehicle sales.  

You can also attach "Groupon" type specials to Foursquare.  If your dealership is in an area surrounded by restaurants, pubs and shopping, then attaching a special to Foursquare is recommended.  When someone checks in at "Applebees" across the street from your dealership on Foursquare a small icon pops up "Deals in the Area".   Perfect place to stick your "$19.99 Oil Change & free tire rotation" special along with the dealership phone number.  

Groupon and Foursquare can be two more "guns" in your advertising arsenal.  But Groupon far out weighs Foursquare right now on exposure.  Foursquare just hit 5 million users.   Groupon, they're really flying.  

Groupon North American Stats