The Paleobet, where every letter is illustrated with an extinct species!
Unfortunately, unlike Pharyngula, I can't reproduce bits of it here. I'd have to paste the whole .gif, which kind of feels like copyright infringement. So I heartily encourage everyone to click through.
I will say I think the cutest is doedicurus, which is either an ankylosaur of some stripe, or an armadillo with a club on its tail.
Edit: There I go popping off before I consult Wikipedia. Wiki says that Doedicurus is a genus of glyptodont, whose closest living relative is the armadillo. But Doedicurus was 5 feet tall and 12 feet long, nose to tail. No mention of whether they jumped in the air when surprised, however.