Steam Box will be interesting, it should be more powerful than the 720 or PS4 and have cheaper games.
Sony has Uncharted and Gran Turismo and MS has Halo and Gears but valve is no push over with Half-Life, Portal, etc.
The first Steambox is already up for pre-order. It'll cost you $999. NO, I'm not joking.
According to Valve that's not a real Steambox.
Not an official one from Valve, but it's still a Steambox.