Foursquare Foursquare is - at least right now - the boss of location-based check-in services. Sign up online and then grab this Android app to get started. It's easy and has simple processes for adding venues and checking in. My only gripe is that you have to check for friend requests manually - there's no alert bubble or anything. That should be a no-brainer. Fix that and this gets a 5-bar rating.

Gowalla Call this one Foursquare's wacky little brother. Gowalla makes the most of the game part of location-based services in this app. It's colorful and plays well with Facebook and Twitter. However, there are a number of bugs in the Android version, the most prominent of which is in the ability to drop and pick up items (part of the game). It doesn't always work, and that's a common gripe on the Gowalla forums. Still, it's fun to play with and is a nice alternative to the more minimalistic Foursquare.

picplz This app is a cute way to add photos to your checkins on Foursquare - or to Twitter if you don't do any other location services. Snap a pic and then you can choose where to send it, and you can caption or tag before doing so. It will automatically check you into the place on Foursquare too, if you want, so there's no need to use both apps when you send a picture.