Stilt-legged Fly - Taeniaptera trivittata
Insecta (Insects) ? Pterygota (Winged Insects) ? Diptera (Flies) ? Acalyptratae ? Micropezidae (Stilt-legged Flies) ? Taeniaptera ? Taeniaptera trivittata

Top row: I would have called this the "semaphore" fly, in that it constantly waves its front legs around as if signaling someone or something. Live adult fly photographed at Hidden Lake Forest Preserve, DuPage County IL USA July 1, 2005.
HERE is a Quicktime video of this fly waving its arms about (.mov extension)