In Crystalsong Forest there are mobs named [link=http://www.wowhead.com/?npc=31041]Dispirited Ent[/link]. What's special about them is that they cast Rejuvination on themselves when they get low on health. I used one mob to get my weapon skill from 1 to about 370. After a while, however, you will get to the point where you don't miss enough and kill them too fast for their health to regen. By then you should only be 20 levels away, anyway.
Works best on a pally, I had Seal of Light up. I assume it would work for any class, though.
Proof:
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