Let's see here...
We got the Old Horde, led by Grom
The New Horde, led by Go'el and Vol'jin
The Dark Horde, led by Rend
The Fed Horde by Margate
The True Horde by Garrosh
...And the Iron Horde by Grom and son again.
Predictions for expansion #6 ' Horde! The Warcraft 4 Horde too!