For warriors, I want a mix of the fanciful and the gritty. I want an armored rhino mount. Something like the Wooly White Rhino, but with armor plates all over it, so heavily armored that it looks like a mound of metal coming to gore you. Like a rhino wearing Onslaught. A rhino wearing Onslaught with Christopher Lee's album playing in the background.
Some classes also come to mind - hunters should get to tame a mount, shaman should get a huge elemental ascendant version of a racial mount (so orc shamans would get a stone worg, while draenei would get a fire elekk and so on) and priests should get angel wings (or in the case of shadow priests, dark angel wings) like Imperius from Diablo III.
So what are your suggestions? What class mounts would you like to see?