I have heard a few references to the synergistic effect achieved when different sweeteners are combined. I know it occurs when you combine splenda with acesulfame K but I was wondering which other combinations do this as well.

Splenda with stevia?
Stevia with acesulfame K?
Stevia with polyols?
Splenda with polyols?
Acesulfame K with polyols?

Also, besides knowing whether or not synergism occurs, I'm also interested as to how much additional sweetness is generated.