You'd want Penance, Holy Fire and Smite as your holy DPS.
But SW: Pain, SW: Death, Devouring Plague and Mindblast are decent shadow DPS.

I am rather partial to Smite, since it heals (talented).
And tend to use Penance the most when questing.

It all depends on whether you want the priest to be the healer, or a DPS/heal support.