Speaking to Polygon, Valve revealed that through the trade show they will be meeting with different hardware companies to show off "multiple" prototypes they've been developing.
“Valve will be at CES to meet with hardware and content developers in our booth space,” said Valve's marketing director, Doug Lombardi. “We are bringing multiple custom prototypes as well as some off-the-shelf PCs to our CES meetings.”
Lombardi didn't reveal much about the prototypes, except that they're all “low-cost, high-performance designs for the living room that are great candidates for Steam and Big Picture.”
However, it doesn't sound like there will be many more announced at the trade show as Lombardi says we should expect to hear more “in the coming months.”
Considering some of the problems Adam predicts with the Steam Box (I really wish we were called it the Gabe Cube) it makes sense that they'd be looking at multiple options.