My one twink was a BE priest for healing. I cannot bring up his armory because he is no longer listed in it. But I was a mix of Holy and Disc. I will try my best to get as close to what my build was ...
Main Healing Build (5/5/0)
I just spammed Renew with this spec and ran around giving PW:F/S to people. At one point I think you could get Imp PW:S, but I don't think you can now at 19. Imp PW:F is a waste of 2 points. 30% may sound like a lot, but your only giving them 8 Stam.
Annoying Healing Build (5/5/0)
Almost the same as the above, except I would spam SW
(rank 1) to try and proc the stun. As a BE priest I also would keep Touch of Weakness (Which, sadly, seems to be removed from WoW) on me at all times. If a Rogue tried to hit me, 10% chance they would be stunned while also losing AP and causing a bit of damage.
I haven't played since TBC, so I am sure there are better builds out there to try. But I loved healing in BG, it was more fun then DPS IMHO.
~Zuty