Evolution

[Confabulator]

Firmly agnostic, but evolution is unquestionable.  Really, if you knew the evidence behind it, there's not one bit of question as to whether or not it occurs. 
From all evidence as of now, it seems like, if there is a god, he is very very unobtrusive.  I.E., he stays very far behind the scenes, and everything runs on real laws of physics.  It makes sense, really.  If you want someone to choose to believe in you or do good acts, you don't just reveal yourself to them, you allow them to make the choice.