Alliance - Cenarius
Female - http://www.blogcdn.com/wow.joystiq.com/media/2007/09/ss23.jpg
Male - http://images.wikia.com/wowwiki/images/7/7e/Son_of_Cenarius.jpg
I think these would be perfect for the alliance and possible even a starting zone by or in the Teldrassil. I understand there would be problems with flight animation and getting on mounts. But Blizzard are very smart, they have overcome a lot of complications and i'm sure they could think of something creative. I also think it would be a good idea if they could have themselves as mounts just like the Worgen race.
Horde - Naga
Female - http://4.bp.blogspot.com/_0fk4iEPAmks/TAWYY0ilDlI/AAAAAAAAApM/qD1aIEBlOWw/s1600/Lady+Vespira+5.jpg
Male - http://casualhuntering.brigwyn.com/wp-content/uploads/2009/07/naga.jpg
I think this would be an interesting class to implement into the game. Of course, again there would be mount complications. I think it would be an idea of having legs on land but able to be in your true Naga form underwater. You could have a racial ability, like breathing underwater and swimming slightly faster.
I haven't really done that much reasearch but I wan't to hear what you guys think :) Can't you imagine it? A cenarius druid and a naga mage?