Enchanters - Clarity (you aren't a proper chanter without it)
Dru - I always consider SoW to be the de facto buff that makes a druid
Shamans - Cannabilize is when you start differing from other classes in a massive way
Necro / SK - FD prolly my favourite acquisition
Cleric - CH, it'll be the permanently memmed spell you have.
Bard - Selo's of course!!!
My favourite AA for my chanter on live was either self-stasis (actually the friendly stasis bug that was on for a while was fun and OP
[You must be logged in to view images. Log in or Register.] ) and Phantasmal Opponent.