Mages:
For a mage who's actually going to spellcast, and not try to be a man in a metal suit, crowd control is rule number one.
The sleep tree is incredibly useful. Sleep is an area affect, no cast time disabler, and it works quite well. Followed up by a horror, it does significant damage, and horror will keep it's single target help for some time. Waking nightmare is more chaos then disabler, but it still helps.
The entire cold tree is amazingly useful. Just take it. It won't get you through every fight, as a fair number of targets are cold immune, but for everything else damage + freeze/slow is too good to pass up.
The fire tree is good for damage. Not quite as useful as hold, but certainly has it's place. Inferno does buckloads of damage, and does not require line of sight - very useful for tossing into rooms before opening the door.
The tree with grease can be useful. The wisp doesn't cost much, and spell power always helps. I think that also has the one that lets you absorb mana from corpses - far more useful then the health version of it.
The runes tree has it's uses - primarily the repulsion/paralyze combo, which requires no line of sight and is a high magnitude paralyze AoE. Great to pull off before an inferno, so they have to stay there and bake.
Force fields - get it. Mind blast is very useful early on, force field removes an enemy from the battle entirely - useful on non-gargantuan bosses with minions. Crushing Prision can stop and then kill most spellcasters, and the forcefield/prision combo is a non-friendly fire AoE damage effect.
Lightning....kind of sucks. Earth is OK, but there are better places to put your points.
