A revolution (right now it’s just protests, but it looks like it might become a full blown revolution) has started in Iran.
It is being organized partly on Twitter #IranElection which is a good place to follow it.
It has broke out over an election that voters feel was (and almost certainly was) rigged.
Police are using force to attempt to suppress the protests (video) and there have apparently been deaths. The army has apparently refused to attack Iranian citizens.
Leaked results that are apparently the real results say Hossein Mousavi was the actual winner.
Protesters seem to be protesting their Supreme Leader (see diagram) in addition to the incumbent president Mahmoud Ahmadi-nejad.
— diagram from WIkicomons
Some high ranking Iranian officials have declared the election void.
Many protesters consider Hossein Mousavi to be the true President.
See also this article