On this blog in the past I have recommended the website TweetSpinner.com as a great free site for increasing your followers on Twitter. No more.
The site just changed their offering. They used to have a free service that was quite good, plus an upgraded paid service with more features. I had used the free service to grow my Twitter followers from several hundred up to over 3,000.
But they just changed it so their free service only allows you to do 2-3 actions per day, making it useless. I wrote to them about it and they said "Thanks for the feedback."