Hello! At the south of Icecrown there is the Argent Vanguard, surrounded by the Valley of Echoes. In the Valley of Echoes there are a large number of Nerubians, and some NPCs that have been recently promoted to level 85 status. If you hit one of these nerubians once, and they are then killed by an NPC, you will receive full exp for killing them, around 1000 each time (unrested and level appropriate; increases with rested exp and a lower level). You can use this for leveling, or you can go there before you're meant to (before, say, level 75) and hit them to try and get more exp. The level 85 guards hit for a disproportionately high amount of damage, killing the nerubians in two hits.
This is my first post here. Please tell me if I've done something wrong. Try not to be an ass about it.