Twellowhood (from the makers of Twellow) uses a map mashup for you to zoom in and find people in your area that use Twitter. As you highlight a country it shows the number of people. When I went to the US it then zoomed into the states layout and each state would then show the number of Twitterers when you hovered. I, of course, zoomed into St Louis, MO to see who was in the local area. Sorting appears to be by the number of followers that they have.
Time to see if there is anyone in your area..