Here's one I need help with. I think this is a wasp, and my best guess after looking around a bit is that it's a type of square-headed wasp (possibly in the Tribe Larrini). But I don't have any experience identifying wasps, so if someone can assist with an identification, I'd greatly appreciate it! It was photographed on 31 August 2012 along a dirt path through a coastal grassland on Bodega Head.
Note the purplish tinge to the wings (the wasp would occasionally flick them) and the complementary orange coloration near the "feet."
Below you can see that most of the abdomen is orange-red. The wasp had a distinctive way of pressing its antennae together and holding them still for a while, and then tapping or feeling with them rapidly.
I liked the white stripes on the inner edges of the large eyes.
ADDENDUM (2 September 2012): Thanks to Lynn Kimsey at UC Davis' Bohart Museum of Entomology for a possible identification. She says that this is probably a species of Tachysphex in the family Crabronidae.