Dig this new HTC patent [via via Unwired View, who also composited the image above from the patent] for a new smartphone design. The basic idea - get a dual slider without having to actually build two keyboards. Looks pretty slick, though I'm not personally a fan -- the whole point of a slider is to be able to completely hide the keyboard behind the screen. With this method, the keyboard is always exposed, you just get to pick the parts that are showing at any given time.
Still and all, it's been awhile since we've seen a genuinely new form factor on a smartphone -- this qualifies.