Hearthpwn

*****UPDATE***** 
I haven't completed a full write-up for the new version, but it essentially plays the same. For legendary cards I have switched to Ragnaros the Firelord and Ysera  as they fit much better into this deck. Prophet Velen relied too much on card combos, was expensive, and too easily removed.

The Holy Priest deck centers around the holy spells in a priests arsenal and focuses on doing what priests do best - healing. When playing this deck remember to heal your minions first before yourself.

• Circle of Healing - combos with Injured Blademaster, Northshire Cleric for card draw and Auchenai Soulpriest for a Flamestrike (board wide, not just your opponents minions).
• Holy Smite - Used for early removal.
• Power Word: Shield - Card draw and giving more health to minions, allowing them to trade up. 
• Argent Squire - A real pain card to deal with, it usually takes two cards to remove. This is a starting hand card.
• Northshire Cleric - A good starting card, but mainly here for card draw. Combos with Injured Blademaster and Circle of Healing nicely.
• Mind Blast - These are finisher cards, you only want these late game, never keep them in your hand to start. Comboed with Prophet Velen these are 10 damage cards (with a coin you can play Prophet Velen and both Mind Blast cards in one turn).
• Shadow Word: Pain - Used for removal. Depending on what you are seeing (more aggro or more control) you may need to only run one of these and two Shadow Word: Death.
• Wild Pyromancer - Used for removal, especially against aggro decks with low health minions. Keeping this card healed and using Power Word: Shield allow the Wild Pyromancer to keep clearing and force your opponent to remove him before playing anything else.
• Shadow Word: Death - Used for removal. Depending on what you are seeing (more aggro or more control) you may need to only run one of these and two Shadow Word: Pain.
• Thoughtsteal- This is essentially a 3 cost, draw two cards spell. It can be inconsistent, but more often than not you will find use from what it gives you. Using it earlier increases your chances of better cards.
• Injured Blademaster - High health minion that combos with Northshire Cleric and Circle of Healing. Playing him and not healing him on the same turn is dangerous, as his low health makes him easy to remove for most classes.
• Auchenai Soulpriest - Sometimes you need to wipe the board with a Circle of Healing, or just use your hero power to help with removal. Players are becoming wise to the utility of this card for Priests. More often than not I find this card being a sink for my opponent,  burning cards normally reserved for more powerful minions, trading minions unfavorably or weakening them. 
• Chillwind Yeti - Everyone's favorite Yeti! Great value card and the 5 health is key in this deck, allowing the Yeti to remove minions and then get healed back up.
• Holy Nova - Mass removal card, also heals your minions and with a Northshire Cleric on the board you get card draw as well. Used with Wild Pyromancer it can be a 3 damage mass removal, very handy.
• Holy Fire - Great removal card, plus it heals you. With Prophet Velen on the board this becomes a huge 10 damage and 10 heal card for just 6 mana.
• Sunwalker - The only taunt in this deck. At times I have tried running Sen'jin Shieldmasta as well but unless you have serious trouble with aggro decks, I would leave them out. This deck handles minions by removing them with your minions and then healing them back up to do it again. This card can also be a sink for control spells so Prophet Velen doesn't get hit instead.
• Prophet Velen - He is not needed for the win, but his combos are incredible. Don't play him unless your opponent has exhausted their control spells and you can use his ability in the same turn in some fashion (i.e. turn 9+).

Weakness: This deck may have trouble with control warrior and heavy control druids.

Biggest combo I've had with this deck: Prophet Velen on the board turn 9, turn 10 use 2 Mind Blast and 1 Holy Fire for 30 damage.

Typical finish: Normally your opponent is weakened to 20-15 or  when you are going for the kill. Using minions on the board with Mind Blast or a Holy Fire.