Time Stop:

This spell enables you to unleash total Hell on your enemies. Do you hate it when you are a victim of Time Stop? Now you can inflict the pain on your enemies instead. Combine this with Improved Alacrity for really total mayhem.

Chain Contingency:

This enables you to store 3 spells of level 8 and below. You can either use it offensively, defensively or as a counter. Either way, it is a good way to unleash several spells quickly.

Wish:

This spell enables you to forgo rest and is best used with high WIS( if your WIS is below 18, drink a Potion of Insight first).

Spellstrike:

With this spell, enemies can kiss their spell protections goodbye, just remember to cast a lower level counter spell like Ruby Ray of Reversal first in case they have a Spell Shield activated.

Imprisonment:

Why cage them when you can just kill them?

Freedom:

The only time you will want to use Freedom is when somebody gets Imprisoned. Best to just carry some scrolls along and not waste a spell slot on it.

Gate:

Trust me, by the time you can cast this, you are already more terrifying than a puny Pit Fiend.

Spell Trap:

Staff of Magi has it and its' version is much better.