Batista relinquished the World Title a few weeks ago because of an injury (a torn biceps, I believe). SmackDown GM Teddy Long held a 15 (or 20) man over-the-top rope battle royal, in which the winner would be crowned the new World Heavyweight champ. Angle made a surprise appearance (not really surprising, as SmackDown needs star power), Angle won the match, and the title.
As for Cena, I dug his character for a few months, but they really need to do something with it. Does anyone really buy the whole "white thug" gimmick?