I cannot recall too many offhand, but I like the one Radioman was using. I wish he'd go back -- the new one is unsuitable to him IMO.
Most of the gifs are clever. I like the image in someone's sig line, where Obama changes into Carter. And strollingbones' is clever too, though I am not always able to see it move. Must be a glitch somewhere.
Oh, and I like my own avatar. God damned Mattel Toy Corp.!