KT

I like the idea of a heal spell that is proactive. Something like this:

2nd level, heals 1d8+2, but doesn't trigger until the next time the target takes damage.

This requires a little planning, because you don't want it to trigger on a 1 or 2 point hit, and it might be inadequate (if the person gets hit for 20). Also, it gives the priest something to do in the 1st round, when no one has taken damage.