Twitter's new kid on the block: FastFollowers - A Virtual marketplace for followers.
If you're desperately looking for a way to build your twitter follower base, here is the nice little site that will do the trick for you.
All you've to do is:
i) Enroll yourself at FastFollowers
ii) Earn credits for following people (Usually from 2 to 5, up-to 10 allowed)
iii) In return, you'll get followers for your earned credits (Tip: You can set the credit limit: as usual 0 to 10. "4" worked fine for me)
Here's a little illustration provided by them:
That's it. Simple but effective. With little time and effort, you can increase your twitter followers base quickly as well as consistently and more importantly ethically. Icing on the cake: It's completely free too (Optional: You may buy credits or get "Featured user slot for a day" - Only if you don't want to follow people).
Get in and reap the benefits.
More details about this program can be found at their FAQ section.
Note: Only today morning I enrolled on this site and already get 50 odd followers. Needless to say, I already took the "Blog about them Offer" too to get 100 credits!