Metachroma sp. (?).
Size: approx. 5 mm. Photo: 09/14/11, 9 pm.

This little fellow belongs to the family of Leaf Beetles. It is probably Metachroma sp. (possibly Paria sp.) This genus has 40 species in North America. 
bug guide (this photo):

Metachroma longicolle.
Size: approx. 3-5 mm. Photo: 06/27/12, 7 pm.

A small leaf beetle named Metachroma longicolle. To me it looks distinctly different from the Metachroma sp. specimen that I have posted above. 

bug guide (these photos):