This.
Agamaggan was an awesome ally in the War of the Ancients (Cenarius went to HIM for help against the Burning Legion), sacrificing himself so that Malfurion could reach the Well of Eternity. According to wowwiki, his spirit currently resides in the afterlife, so it shouldn't be too hard to bring him back.
Plus, he can do this:
Giant hoof stomp? Acid breath? Thorn rain? Sounds like my kind of boar.
http://www.wowwiki.com/Agamaggan
Edit: And this little tidbit adds all the more reason:
In conclusion, I want Mr. Superboar back. Now.