Repipta taurus (Red Bull Assassin).
Size: approx. 10 mm. Photo: 04/19/12, 9 pm.

The Red Bull Assassin (Repipta taurus) can be easily confused with other assassin bugs such as Zelus longipes. A distinguishing mark are the projecting spines on the thorax of R. taurus. It can be found in the Eastern and Southeastern US as well as Texas. 

bug guide (these photos):