At CES, we saw a few companies touting their Steam Machines, but none of the ones we met had a controller to show. Everyone was excited to launch one soon though, but it looks like there's going to be a delay.
Valve has posted that they have a wireless prototype of their controller working and testing it out with various individuals. Because of the improvements and work continually being done, 2015 will be the year Steam Machines get the roll out.
Now, this news is going to certainly disappoint those wanting to pick up one of the Steam Machine variants, but it's imperative that Valve gets the controller right so that it's a good experience. I've read that some people aren't really digging the touchpads in place of analog sticks, so more work might need to be done on that end to ensure success.
At least you can install the SteamOS right now if you want your own type Steam Machine. For now, we'll have to wait until sometime next year to be able to purchase a complete setup with the unique controller in hand.