Dispel Magic:

Your party members are afflicted with malison, stunned, dominated, etc... Dispel Magic to the rescue!

Melf's Minute Meteors:

It is a +5 enchanted weapon, useful for disrupting Mages and finishing off Trolls thanks to its' elemental fire damage and can be hurled at a rate of 5 per round.

Slow:

A slow moving target, is an easy target. Good against low to mid-range enemies, this spell greatly dimishes their attack capabilities, and if your fighters are hasted, the battle will be over in no time. This spell is a good battle starter, and it covers an area too.

Flame Arrow:

Absolutely devastating in a Spell Sequencer. You get 1 bolt for every 5 levels of the caster, up till a maximum of 4 bolts. Each bolt deals 1d6 of physical damage and 4d6 of fire damage. So, at level 20 and beyond, you are dealing 20d6 damage per shot. Put 3 of them in a Spell Sequencer... and voila! 60d6 damage!!!! Note that the battletext can be misleading, the game bunches up the fire damage in pairs. So in reality, the damage seen on the battletext window is 1d6 physical damage and 2 sets of d12 fire damage per bolt. This spell is great against Beholders and if you are fast enough, you can destroy mages before they cast their protection spells.

Skull Trap:

Use this as a trap and it will serve you well.

Remove Magic:

I thought at first that this spell would be good, but its' success rate is horrible.