I don't own a PS3, but I'm looking forward for this on the PS2. Star Wars: The Force Unleashed is set between Star Wars Episodes III and IV and lets you play as Darth Vader's secret apprentice. This will be released on spring of 2008. By then I should have a PS3

The story revolves around Darth Vader's secret apprentice, when Vader learned that Emperor Palpatine is just using him to rule the entire galaxy. The timeline of the story is between III and IV, the time when the Jedi are being wiped out. Several characters from the Prequel Trilogy are set to appear in the game. It is said to have multiple endings. But I believe you have to play as a bad guy (Sith) in this game.
Check the newest trailer. That one's cool.