During the month of March, participating Chipotle locations are offering an order of FREE chips and salsa on Saturdays and Sundays when you check in using your Foursquare account. To get this deal, launch the app on your mobile device and look for the location nearest you with the “special” banner, check in, and the coupon will be revealed; present the digital coupon on the screen to your cashier to get your freebie. Click here to view all the participating Chipotle locations! 
(Thanks Red Plum)