Amongst the hundreds of mashups and utilities for Twitter, there are very few that I find particularly useful. In fact, most of my interfacing with Twitter either takes place in my feed reader or in a GTalk window. Matt King's TwitterWhere is a definite exception to the rule, however. TwitterWhere is an elegantly simple tool that allows you to generate an RSS or XML Feed that will provide you with Tweets around a given geographic area.
Not to be confused with TwitterWhere.com (a tool allowing you to easily update your current location), in Matt King's TwitterWhere, search criteria can be entered by city, state, and postal code, then designate the range in miles you wish to include. Once search criteria is entered, you'll be given links to feeds in RSS format, or in an XML file in the format of the Twitter public timeline.