GeoChirp pleasantly surprised me with the sleek interface and immediate usefulness. You get immediate function without logging in. It guesses your current location and shows it on the map and starts to bring in tweets at the bottom.
You are able to enter any address, number of tweets and miles radius. You can also simply drag the placemarker around on the screen to another location and zoom in and out. If you need to see more tweets and less map once you search you can click the tiny Map button at the top and it will minimize the map area.
Logging into the site utilizes oAuth and brings your Twitter bio and last tweet to the bottom right.
If you want to find and see any tweeting within some radius, this is certainly a great mashup.