Twitter now has lists, which are in effect subgroups of your followers that you set up for a particular reason (and a follower can be assigned to more than one list). Lists can be public (and can be followed as if they are Twitter users themselves), or kept private.
For example - I set up a public list that shows the Tweets of my followers (people and companies) who are interested in eLearning:
Please feel free to follow the list and/or me - if you do follow me, and are interested in eLearning, I'll add you to the list!