With the daily quest http://www.wowhead.com/?quest= 14102 you can summon the needed mob with the given item.

He gives 500xp unrested (1000 rested) at level 79 when in group with a 80 toon. You can summon him again once he is dead… again and again and again

lets say it takes 5 seconds to summon an kill him.(prob. less)
that would be 12(times a min) x 500(xp unrested) x 60(minutes)= 360.000 xp/h
that would be 12(times a min) x 1000(xp rested) x 60(minutes)= 720.000 xp/h

All you need is a friend who can get this quest. (exalted with Silver Convenant and have Crusader title). And i kind of gets boring after killing him 1000 times

The entrance to the cave can be found at, 43,25 above icecrown.

Use this method with mobtagging and u get 2300 per rested kill and 1150 per unrested
12x 2300×60 = 1.656.000 xp/h rested
12x 1150×60 = 828.000 xp/h unrested