The Tiger Swallowtail butterfly (Papilio glaucas)http://en.wikipedia.org/wiki/Eastern_tiger_swallowtail
This is a Female. The way you know this is by the amount of Blue at the base of the lower wings. The Male is blackish in those spots,. She had just come form a Tiger Lily, as you can see the orange pollen on her back, and spots of it on her upper wings. She is on Hosta Bressingham Blue, a Hosta leaf here resting, or posing .
I never get bored of seeing these in the garden. In an earlier post I put a black version of the same butter-fly. As mentioned before there are two variations of the same. However the Male is always Yellow and Black