DivX, a video codec, is usually available in a free basic version and a pro version for 19,99€. At the moment, the pro version is also available for free.
The DivX website doesn’t tell for how long the offer will be available. It only says “for a limited time”. The catch is that one has to enter an e-mail address upon registration.
Personally, I prefer the free open source alternative XviD anyway. 🙂