Great Spell Combinations

[Anabstercorian]

Spectral Hand plus Empowered Touch of Idiocy can make life hell for a caster in a hurry.

This isn't really a combination, but Empower Spell plus False Life can get you some 30 temporary hit points. That's a lot.

 

[MadScientist]

A good low level druid combo is summon swarm and briar web (MotW). Characters cought in both pretty much take damage no matter what they do.

Edit: This combo also workes with entangle, but isn't quite as effective.

 

[Psychotic Jim]

Ghost Sound and Silent Image cast in coordination with each author to appear to be the same illusion.

 

[Stormrunner]

Fly + Improved Invisibility. Each round, take your movement after you cast your spell. Opponents have to pick, not just the correct square on the ground, but the correct *cube* in a 3-d hemisphere in order to hit you, unless they ready an action to fire when you cast (and even then you can avoid being targeted by using spells which don't produce a visible line/cone extending from your location). Especially good for bards, who can hover out of danger and sing (singing isn't an "attack", so even regular Invisibility will work).