Note- As of June 2009, Torsten Dikow has just published a revision to the Asilidae, check this page for some details. Basically, for GA, Apocleinae has been moved back into Asilinae, Laphystiinae has been placed into Laphriinae, and several genera have been moved into a new subfamily Brachyrhopalinae.
Here are some useful links concerning asilid identification or biology:
Steve Collins has just created a new robber fly ID site based mostly on Florida but full of great information about southeastern and other robber flies, I highly recommend it! robberfly.org
Asilidae Fritz Geller-Grimm's excellent website for all around information and many links
Raney Robbers Herschel Raney's robber site, lots of good info, geared partly to Arkansas, plus an Eastern species key.This site is being published in March 2020, and many of the pages have been brought over from my old site but are not yet cleaned up from transcription issue... please be patient with me!