Twitter has a great little widget that you can add to any web page to display a Twitter search. This allows you to creating stream of information about any topic of interest and post it in your website. In a CMS-based site, such as WordPress or Jooma, or a social platform site, such as Spruz, you can add this widget to a global area, so it automatically shows up on every page.
You can find the widget here.
For example, if you'd like a running commentary of the Seattle Sounders, you customize the widget as follows:

However, there is a bug in the widget that has been acknowledged by Twitter: you cannot create a radius search around a location and insert it into the widget. A radius search on Twitter allows you to find all tweets within a zip code or city name, such as "near:Tacoma within:15mi" or "near:98501 within:20km". This is unfortunate because the radius search is a great way to find out what people are talking about in your area.
As it turns out, there is an alternative: Geocodes!
Geocodes include the latitude and longitude of a location. So, for example, let's say I want to do that Tacoma search I listed above, you would enter the search as follows: "geocode:47.252877,-122.444291,15mi".
If you don't happen to know the geocode of the location you'd like to search off the top of your head (smile) try this handy tool at iTouchMap.com. Simply enter the address, city and state of the location (or just the city and state if you want the geographic center of a city), and you'll see the exact geocode.
Here's a custom widget for my home town, Menominee, Michigan:

But here's the really cool part: you can use geocodes with search keywords to create a custom search. For example, here are a pair of actual widgets I've created to follow the twitter streams about the playoff game between the Seattle Seahawks and the Chicago Bears next week:
Trash Talk on Twitter: Bears Vs. Seahawks Playoff Game
Thanks to the following thread for helping me find the answer to this problem: http://code.google.com/p/twitter-api/issues/detail?id=1401