Splitting Arrows can hit more than one creature, even friendly ones if you are not careful. Hell Spikes does area damage, but needs to be maxed for best use. Elemental Hail and Poison Cloud are also area effect spells.
SpellShield and Aura of guarding last indefinitely if you do not get hit with damage.
Shadow Warrior vanishes after striking; sort of a slower, less effective ranged attack, though I think I only tried it at level 1 or 2.
True Shot is currently broke.
I have not checked gamefaqs.com, but;
The Locus Inn - Skill System (individual paths, or a skill table for each class)
RPG Vault - Divine Divinity Skills XI (links to other skill sets at bottom of page)