Alienware listed among them
CES 2014 is the big coming out party for Valve's Steam Machines. I'm seeing one bright and early tomorrow morning here in Las Vegas, coming from Digital Storm. Later tomorrow evening I'll be attending Valve's press conference where we expect that Valve will announce other partners.
Engadget says that they already know of 12 official Steam Machine hardware partners:
We should expect that other parties will be listed tomorrow beyond these, but this is a pretty good lineup already. We've already heard from other partners, but we'll sit tight on our embargoes.
Check back Monday evening around 5pm Pacific for the full news from Valve's press conference.