Voted for:
- Mage's Sword (cast it and let it fight on its own, while you cast other spells. It is good against incorporeal creatures and has a quite good attack bonus)
- Spell Turning (comes in handy when you're targeted by Greater Dispelling, Horrid Wilting,...)
- Greater Teleport (simply useful, even for the whole party)
Prismatic Spray is also a nice offensive spell, but allows SR and save. Waves of Exhaustion allows SR but is quite effective against non-constructs and non-undead opponents.
Forcecage is too expensive, IMO, burning 1500 GM per use may deplete the wizard's cash quickly... Limited Wish is nice, but losing XP too often hurts.