The latest Steam marketing message is up, noting a number of game deals and the availability of X-Com: Terror from the Deep for $2.45. There's also this on Half-Life 2 Episode Two:
Right now, we're working hard on putting the final parts of Episode Two together. Early on during development we spent a lot of time working on concept art of key areas of the game, so that everyone on the team could share a vision of what the final game would look like. The three pieces below are some examples of that work. Once the game is released you'll be able to see how these concept pieces were eventually turned into the final product.