TweetAdder

TweetAdder will increase your twitter followers with people that match your preferences and interests. Searches include by location (anywhere in the world), by language spoken, by tweet keywords, by another profiles followers, or people being followed by another. Sends out automated follows of these exactly matches resulting in a very high return of new twitter followers who will then receive all of your twitter status updates (tweets).

Limitations:

250 Follows, 10 Tweets, 10 Direct Messages