None of Michael's suggestions would really work -- the Taunka are almost a completely different race, the Forest Trolls can't be very happy that we've killed their leader, and neither the Dark Iron Dwarves or the Iron Dwarves are very friendly to either Horde or Alliance. But there are possible variants out there -- the Zanadalar tribe might have some members interested in joining the Horde, and certainly the Mag'har Orcs are friendly to players. Alliance doesn't have as many options come to mind, though all players are Bronzebeards, I believe, and surely the Stormpikes are Friendly by now.
We've got new hairstyles coming in the next expansion, of course, but it would be nice to vary up the races a little bit, and have even different backgrounds within the race choices. RPers would love it for sure, and even for other players, it would give a little more meaning and power to playing through the various racial areas in the game.