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.
"Yes.
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,
Community Coordinator, via the
official forums.