Does every game have to have a comic now? I don't mind a comic, but sometimes I just want the game, and none of this stringing myself along with prequel content and backstory in a different medium. Anyway, I'm probably being a miserabilist. So there's a Dungeon Siege III tie-in comic due from Dark Horse, spanning three issues - this is good news if you're into DS lore, I guess.
You get a full-length print copy if you pre-order the game from certain stores (Wal-Mart specifically; not sure about non-US territories yet) or you can read one of its two 10-page stories for free on the magic internet here. You'll need to create a Dark Horse Digital account. Should you bother? No, not really. It's just pretty bland exposition and plot setup for the game, really. But it's free! That's important, right?