This is the best I could do photographing him. He wouldn't pose for me. :=(
Possibly a Spicebush Swallowtail http://davesgarden.com/bf/go/94/ or a Black Swallowtail http://davesgarden.com/bf/go/6/
Definitely one of those two. Here's another image
And one more
Don't know if those help. They don't seem to help me.