I'm not sure if this has been mentioned but Haste is disgustingly good through level 20 or so.
Pickup a 2H of any kind for a Warrior/Paladin/Druid/Shaman and slap
Iron Counterweights on them. Choose a level 4, 10 and teens quality BOE weapon and get ready for some fun. If you're really interested in power leveling, grab a
Blood Elf Bandit Mask from Azuremyst Isle and slap a Libram of Rapidity on it. That way you can use the item again and again on different characters or help friends level their alts/twinks. I've been leveling a twink Druid and I believe at level 10 when I first learned Bear Form, my attack speed with +30 Haste was something like 1.4. That's insane.