Foursquare The game I love to hate. I've met connections, seen where friends are, etc. with this game, but have also battled for Mayorships and cheating is quite abundant. Still, it's the best one out there overall I hate to admit.
Yelp In addition to restaurant and business reviews, Yelp has begun adding a check-in feature where you can see the different places that your friends are visiting and commenting on as well.
Gowalla *UPDATE! It seems Gowalla has integrated their stamps and check-in's with FourSquare. Perhaps time to take another look with their latest update.
yet another game to share the different places you visit with your friends. Same same, it pushes to your Twitter and Facebook if you'd like.
One caveat is that GoWalla keeps crashing/freezing on me and so I've uninstalled it.
Waze social GPS maps & traffic Fun little GPS game where you can earn points by reporting traffic conditions or going over certain areas. However, I think it could be a bit dangerous and best played as a passenger while someone else is driving. 2plyr team kinda game
Whrrl Seems to still be a bit buggy and this is another such geo-location check-in game to discover new places and share the different locations you've visited except you can join groups of people based on common interests