Have An Extra Pet That Levels With You (Alliance Only, Worgen)

Well, There is a quest in the Worgen starting zone named From the Shadows and gives you an item, Gilnean Mastiff Collar 

If you get this quest, Then escape the worgen starting zone, ( if you dont know how to escape the worgen starting zone, Check a video out on youtube, Try Trokair's method, Works very good, And still works for even me. ) 

You will still have the quest item, and can summon a dog that levels with you until you reach your limit, Lvl 85, (MoP Even lvl 90 )

Here is Trokair's video if you need it: