Part three of the steam announcement has come and gone, with Valve announcing a gamepad to go with the OS and Console - Personally i'm not sure what to think of it.
The controller has been built from the ground up with Steam OS in mind, enabling it to support the complete Steam catalogue, Valve has said they have fooled older games into thinking they are being played with a keyboard and mouse.
The controller certainly looks unique but it seems to have some nice features built in. It has dual trackpads, haptic feedback, a touch screen of course as well as much needed buttons. The reason for the whole new design is the push towards openness and hackability, with the SteamPad designed to be just as hackable as the SteamBox.
One of the nicer features is the ability to share button configurations, as you would expect the games that don't support a controller natively will need to be configured, with this you will be able to select from a list of the most popular user generated configurations.
If you want to know more check it out at http://store.steampowered.com/livingroom/SteamController/