Foursquare fiends rejoice as amBar and BeerVault (Four Points by Sheraton Hotel, Sukhumvit Soi 15, 02-309-3113) offer a free round of their signature cocktails when you check in with minimum of 6 other friends. Don't have that many friends? Go there on Sun-Tue and check in from 6-9pm to get a free cocktail or a beer for yourself. Or, better yet, oust all the others and become a mayor at either venue to get 25% off drinks (except during the happy hour) at that respective bar.