Foursquare The granddaddy of them all and a must-download for you. Since they've been around for the longest and have a strong user base, they also have the most specials at local businesses waiting for you while you're out and about.

Gowalla This one came out about the same time as Foursquare, and while it's easily the better looking one, the best thing in it for you is a cool custom badge to slap on your Facebook wall.

Loopt I keep this one on the phone for their random specials - they don't have much of a user base, but occasionally they release some incredible deal. This one will alert you when a big special is nearby when you check in within a certain radius - after that, it's up to you to come running!

SCVNGR More location fun, this one mostly around scavenger hunts and discovery - fun for curating your favorite spots.

Yelp While Yelp is the home for great recommendations and discovering new places, it's also a check-in app. Check in enough and you can become the Duke!

With Less about more locations and more about - just as the name says - who you're With. Check in with others and post photos of your meeting to keep track of your experiences. Pretty beautiful app, too.

Localmind If a check-in can be a question, then Localmind is how to do it. If you're confused already, don't worry - it's a unique concept. Localmind lets you post a question at the place where you are - maybe something like "Are there any good coffee shops around here?" and automatically alerts others using the app that are in your area. If locals give the best answers, this might be just the place to find them.

GetGlue Checking in goes truly crazy with this app, far beyond just places. GetGlue lets you check into shows, movies, celebrities and many other brands. Plus, you can earn some nifty virtual stickers along the way.

Miso - Social TV A check-in app focused on TV - just tell it what you're watching and share around with your friends.

IntoNow from Yahoo! IntoNow is the perfect app to have open while you're watching TV. Just hit "listen" and it will detect what show you're watching (even live TV) and post to your Facebook or Twitter accounts.