motherboard voltage used for cpu?

I have had the hardest time finding this information. Even on the board I was running I could not find out that it used the 5v channel from the power supply to feed the cpu (untill someone told me on a forum). That mother board has fried so I am looking for a new one. While it is not a deciding factor, I still would like to know what voltage is being used in relation to the power supply. Is there a most common voltage (I am kind of starting to believe that most mother boards use 12v but I could be wrong). Is there a good place to find this info or a good search term to use that I am missing?
On a side note, same question for agp video cards.