Streamd.in is a Twitter client with a difference - it has a Google Map attached. There have been a lot of Google Maps mashups created to show Tweets on a map but this is the first one I've seen that actually also works as a proper Twitter client.
Streamd.in lets you read Tweets from the people you follow, view your direct messages, view any updates that mention you and post a Tweet. In fact it does pretty much all that you can do on Twitter.
The big plus for me however is that it also has Google Maps. This means that you can not only catch up with the people you follow but you can also view Tweets from around a particular location. You can share your location with streamd.in to ensure the map centres on your current location. You can also pan the map around to view Tweets from other locations around the world.