Tweet Blender Twitter Widget
This blog uses Tweet Blender - a free open source plugin developed by Kirill Novitchenko that provides several Twitter widgets so that you can: show your own tweets, show tweets relevant to post's tags, show tweets for Twitter lists, show tweets for hashtags, show tweets for keyword searches. Multiple widgets on the same page are supported. Tweet Blender Twitter Widget can combine tweets from multiple sources and blend all of them into a single stream.
For more information see Tweet Blender Twitter Widget Homepage or Tweet Blender WordPress Plugin Page