The realms Illidan, Mal'Ganis and Warsong have the option to transfer to the Zuluhed server. Aerie Peak, Area 52, Moon Guard, and Zul'Jin have the option of transferring to Muradin. On the Oceanic side of things, the servers Barthilas and Frostmourne may transfer to Dreadmaul if they so choose. Forum links embedded for your new-home-researching convenience.
Remember, these transfers are only open until September 10th or until their transfer quota is met. If you're interested in moving, do it as soon as you can so you don't miss out.