What does and doesn't stack?

I believe that all bonuses stack with each other...someone correct me if I'm wrong.

Anyone know?

Im really curious about +speed items and +regen items.... Does anyone know if its a flat stack or diminish?

There is a maximum speed and a minium speed. Once those extremes are reached it can't go higher or lower. Armor stacks with diminishing returns, everything else I believe stacks as you would expect it to. Buffs should not stack (for example the helm that gives a -25% spell cooldown aura, only one can be active even with multiple Demigods having the hat).

But when it comes to stats, Everything stacks.

If the item says it will give you 10% movementspeed, thats what it will do, no matter how much movementspeed you had before.