I've heard of promotions that give you in-game items or maybe even a poster. But only Richard Garriott would give you the opportunity to send your DNA into space or have your MMO character data uploaded and stored on the International Space Station.
You can check out his Operation Immortality and read more about it. You do need a Tabula Rasa account but you can still be elgible with the free trial. Each week, 8 Tabula Rasa players will be selected to have their DNA sequenced and the data uploaded to Garriott's Immortality Drive. And when he travels to the International Space Station in October, he'll be taking that data with him to store there.
Even if you don't get your DNA selected, Tabula Rasa players have the opportunity to have their character data uploaded to the Immortality Drive or leave a message to be stored on it.
In this Wired article on his journey to space, Garriott also mentions that he has ideas for an MMO that "shares more in common with Ultima Online than today's popular virtual worlds."