Well if you have a group of toons that have not completed these quests then you can use them to summon a bunch of mobs that you can endlessly grind for XP.

From 72+ you can do this quest in Dragonblight: http://www.wowhead.com/?quest=12261
You can use the Destructive Wards every 1 minute to summon a crystal that mobs spawn and run up to and attack (all melee mobs). The more crystals you have out the more mobs that spawn, although there is some limit it seems. Each person on the quest can have 2 crystals out, in a group of 3 with 2 on the quest, we grinded a level in just under 3 hours here (rested). Doesn't seem too fast but I bet in a full group of 5 with 10 crystals out it would go quick, especially if you're mobtagging to level just 1 char up. Probably faster than the Onslaught camps!

and from 77+ this quest in Icecrown: http://www.wowhead.com/?quest=13295
Just use the spinal fluid, kill the mobs, and fail the quest.