Eastern Tiger Swallowtail

These are the very large yellow butterflies zipping around our yards. See the tail for the interesting colors. Clicking any photo reveals the details.
The males and females are different but also have a dark morph you have likely seen too:

Dorsal and ventral sides of Papilio glaucus adults

1. Dorsal male
2. Dorsal female
3. Dorsal female (dark morph)
4. Ventral male
5. Ventral female
6. Ventral female (dark morph)
From: http://en.wikipedia.org/wiki/File:Papilio_glaucus_adults,_MM.jpg