The concept is simple: the way to meet new people is to step outside of your comfort zone and try something new.
How about a dance class? Learn to rumba, cha-cha, or ballroom dance. Every city is full of dance studios offering classes nearly every day of the week. Then take your new dance moves and spend a night on the town showing off what you've learned.
Dancing not you thing? Try a cooking class instead. Classes are typically held in the evening and most cooking schools offer specials if you bring your friends. Grab a group of friends and learn how to make something new too. If you don't have anywhere to show off your new recipe, bring it into work. You'll score points with your co-worker. Plus who knows, they may rave to their single friend about what a fantastic cook you are.