While we still don't know exactly what the pandaren mount is going to be, that has not stopped the internet from speculating. Malchome over at mmo-report.com thinks that the pandaren mount should be a keg cart pulled by some sort of mule or yak. Epic versions could be more intricate, much like the goblin trikes gain complexity as their quality increases. There is a wonderful little mock-up drawing of the keg cart in the post as well. I love the idea as a mount in general, not even just for pandaren, especially with the Brewfest connection.
Personally, I believe the pandaren mount is going to be some sort of frog or amphibian. We don't have many of those types of creatures as mounts in WoW, and it gives the artists a chance to do some really cool ornamental graphics on some sort of creature. There is a Chinese symbol for prosperity called the Chan Chu, a three-legged frog creature that carries a coin in its mouth, that could be adopted to be the pandaren mount. Giant Chan Chu frogs might share the land with the pandaren, much like the kodo beasts roam the plains of Mulgore with the tauren.