Ageniella sp. (Spider Wasp).
Size: approx. 10 mm. Photo: 08/07/11, 5 pm.

This spider wasp belongs to the rather larger genus Ageniella which has 35 species in North America. A. conflicta has striped wings like this wasp. It reminded me of a velvet ant but that's wrong (like many of my guesses). The small photo shows a side view of the same specimen. 

bug guide (this photo):