twtAd is a system that enables you to monetize your tweets. Based on a similar concept to Be-a-Magpie, twtAd pays you a few cents for every click to the URL from the link posted on your Twitter page.
Once you reach $20, you can withdraw the amount via PayPal.
The system has been up for only a few months, and has gained over 100,000 Twitter users and is growing rapidly.