The Celestial Steed has been added into the game and it looks to be an all around mount that can function is a ground mount in the old world and a flying mount in Outland or Northrend. There are no screenshots of it yet, but my guess is that it's a horse with wings that could double as a constellation. Check out the picture above for an idea.
Tailors also get another Flying Carpet to create. The Frosty Flying Carpet is purely a flying mount. It's only usable in Outland and Northrend (until Cataclysm.) In order to ride it, the tailor needs to have at least 425 tailoring.
The Celestial Dragon has been added to the game files, but we're not yet sure where it comes from. It certainly looks pretty though. I'd speculate that it could be a seasonal boss drop, or maybe it is the next reward pet after hitting the Lil' Game Hunter achievement (the 100 pet mark, perhaps). Kudos to MMO-Champion for the shot!
Engineers, you may wish to stock up on the mats required to build a Pet Bombling and Lil' Smoky companion pets. Why? They won't be bind on pickup in the next patch.