Tweetscan is useful web app for tracking twitter. Lot of people post tweets to twitter on latest happenings, breaking news etc. Suppose you want to keep up to date with Microsoft, Yahoo deal, you could search with these terms and see who is posting this and what’s new.
You can also search twitter by combining keywords and users. In this case what techcrunch is posting about Microsoft and Yahoo deal.
Search results are organized with the latest tweet on top. You can subscribe to RSS feed for the topic of your interest so you don’t have to open the site all the time. If you prefer to use searching install the browser search plugin, it works with both IE and Firefox