A poster on the forums asked about whether people would like to see spider mounts in the game. It's true he was just asking out of boredom, but to me this actually an interesting question. We have the Black Qiraji Resonating Crystal, of course (pictured here, courtesy of Wowhead), but that's more or less impossible to get now, and it's not exactly a spider in any case.
What sorts of new mounts will there be then? Nethaera responded: "I couldn't tell you what possible new mounts there will be. :( Perhaps a little further along we'll have information on more of the fun features that are getting added in with Wrath of the Lich King."
What mounts would you ask Blizzard to put in the new expansion? Flying machines are already going in at some point, and bats and hippogryphs have already been mentioned. How about rideable owls? For land mounts, maybe you could ride on the shoulders of your very own yeti! Better yet, what if we could pilot our own slow, yet moveable siege weapons?