Well, I'm interested in the Achaemenid Empire and it's society (they seemed to be doing quite well before Alexander showed up) and was wondering: What would the consequences be if they won the Greco-Persian wars, say with a POD in the Battle of Marathon? Obviously Philip and Alexander would be butterflied away (and probably most of western civilization, in the far view...) but could they hold Greece? Would this lead to a stronger, longer lived empire? What city-states could raise in rebellion (Sparta comes to mind) and be sucessful?
Also, without an strong greek empire, the persian culture would be dominant, affecting future empires (like Carthage and Rome, if not butterflied away). How far could it expand?