Peer Review, Portal 2's first piece of DLC, is now up on Live. According to the blurb: "Featuring a devious new co-op track that continues the story of Atlas, Peabody and GLaDOS, the DLC also includes both single and multiplayer challenge modes, plus leaderboards so you can compare your portal placement and time scores with the Portal community." Cost? It's free. More from Nelson.
Also, if you are new to Portal 2, you can get the game for $14.99 through Steam from now until October 6.