I'm a sucker for winged armor, so the paladin set (embedded above) is my favorite by far. The shoulders on the rogue set are fantastic, and the shaman set seems tailor-made for trolls. Unfortunately the mage, warlock, warrior, and monk sets are still missing from the lineup, so we'll need to keep an eye out for those in future beta patches.
You can see a sampler of the currently available armor sets in the gallery below, but I do highly recommend checking out the 3D model viewer over at Wowhead as well. Wowhead has a whole slew of other models you should check out at the same time, such as mounts, more weapons, and miscellaneous quest reward gear sets.