We finally have the Albino Drake!!!! The acheivement reward for Leading the Cavalry. 50 mounts isn't impossible to achieve, and is definitely easier for those that are collecting now with the Tournament mounts available and more dungeon drops that have been added, but it's not a cake walk!
Next stop Mountain of Mounts - 100 mount achievement!
** List of all currently available mounts and Patch 3.2 changes - Wowwiki/mounts or warcraftmounts.com