Biggest "gamechanger" spell/ability

[Landis]

I was just thinking about this last night while watching my mana regen crawl.

What does everyone consider the biggest "gamechanger" spell or ability? What spell do you look forward to so much because it makes leveling significantly easier/faster, or makes the game much more enjoyable?

The only class I've leveled to a high level is an enchanter, and without a doubt I would pick clarity and thus level 29 as THE level to reach. After that, everyone loves you so getting a group is easy, and soloing is that much less painful.

For shaman, I would guess cannibalize.
For druids/wizards, ports?

What do you think?