BlastFollow enables you to follow Twitter users who share your interests en masse. This is accomplished by searching for users who have tweeted with a particular hashtag recently. For example, if you are interested in ISTE 2010 conference, you may want to search for users whose tweets have included the hashtag "#ISTE10". This would be useful if you are using Twitter in your classroom for students to follow a particular class thread.
Finding excellent websites requires hours of surfing through okay and not-so-good stuff. This page allows you to benefit from my hours of surfing over ten years.