Following too many accounts? I hear ya. In fact, I hear ya so much I wrote a script to unfollow all the accounts that aren't following me.
Unfollow simply hits Twitter's API using foauth.org so as not to do the whole OAuth song and dance—you'll need to sign up with them and authorise your Twitter account first.
./unfollow.py <foauth.org email> <foauth.org password>
Unfollow will print authentication or rate limit errors. Run it a few times just to be safe.
I couldn't be arsed doing pagination, so Unfollow only checks the first (however Twitter defines that) 5,000 accounts you follow and followers.
Don't blame me if anything goes wrong.