Many of the spells already listed are great for countering mages
My thoughts:
Casting Shatter focused around the mages arcane focus (say, staff or wand but HOPEFULLY a crystal ball,) would be pretty nasty. No more arcane focus, no more spells! (One of my favorite spells!)
Detect Magic: Necessary for any Mage Hunter worth their weight. Millions of uses, and would greatly assist you in hunting them down especially well because mages hide through magic (Disguise self, alter self, pass without trace, etc,).
Fog: There are uses for this, more like a trump card rather then a straight strategy. Still VERY nice, especially if you supplement your fog with melee or ranged capabilities.
Invisibility or See invisibility, depending on your general strategy, enemy composition, and approach to tactics.
Sleep, Alter Self, Dispell magic / Counterspell, Fly, Lightning Bolt/Fireball (for Mage's minions,) all very nice. Obvious uses. Certainly Alter Self / Disguise self, if your character would approve of such spells.
Personally, I might supplement your spells with a good Longbow or Longsword. The best way to kill a mage is with a Ranger locking onto them or a melee in their face. Even if that melee is you, a SORC, just putting pressure on them with a melee personality or tactic can really give you an edge (since you will likely lose the edge in spellcasting, due to less known spells, which is less options, in and out of a combat situation). I'm not saying multi-class into Fighter. I'm just saying keep your options open, as much as possible.
Hope that helped, at least a little.
- Holly
