• by Mark Walsh  @markfwal, May 17, 2010

Expanding on its partnership with Foursquare, Starbucks has begun offering its most loyal customers a $1 discount on a Frappuccino. Starting today, the "mayor," or person with the most check-ins any Starbucks location via Foursquare, can earn the new reward through June 28, according to Mashable.

In March, Starbucks began rewarding frequent customers with a Barista badge after checking in to five separate locations. But the discounts offered to mayors of individual stores marks Starbuck's first step toward providing tangible benefits to customers on Foursquare.

And it won't likely be the last, with the social location startup telling Mashable it expects Starbucks to continue experimenting with mayor rewards on a regular basis. Besides free or discounted drinks, the coffee chain has previously said it plans to use Foursquare to offer other prizes including invitations to special events and online reputation scores.

Foursquare is also working with other big brands like Pepsi and Tasti-D-Lite to build virtual loyalty programs around its location-based service. Rivals such as Loopt and Brightkite are pursuing similar partnerships with Starbucks, Best Buy and other major retailers as competition in the space heats up.