"Yes.- Phreak, Community Coordinator, via the official forums.
You can never stack the same item, but different items' unique passives will almost always stack. Movement speed (from boots) and a new stat coming in the next month or so are the only exceptions AFAIK."
Phreak teases use with a new stat.
Posted on Sunday, March 20, 2011 by Moobeat
In a recent thread where someone is asking about CDR items stacking, Phreak dropped us a little teaser. What could this stat be? With all the rage pointed towards heavy CC, a la Sion and Taric, that is creeping on the forum might we see more CC reduction items? Or perhaps something more off base like Energy regeneration? I really don't know but he has successfully peaked my interest.