Tournament decklists give us the decks of top players with decks that have survived trials by fire to win. So they're a great place to start. Team liquid is a good source - here are the decklists from the third TL open. Blizzcon's Hearthstone Invitational was spectacular and memorable and you may want to look at the decklists from there too although those are older and, I believe, not quite so tested against tournament opponents.
I wanted a Priest deck just now for my daily quest so I chose to steal SpecialistSC's Mystyle deck from TL Open 3.
However my problem was that I'm not a "whale" so I needed to analyse the cards I didn't own and select suitable replacements.
By rarity the deck is:
Even though I'm missing a lot of the high end stuff there's a lot of the deck that is free so anyone can take this deck and adapt it.
Let's look at the cards I'm missing:
Argent Commander (1)
Holy Fire (1)
Ragnaros the Firelord
OK, that's not too bad I own 22/30. Let's see what I can swap in:
Mass Dispel for Thoughtsteal - similar cost, trades card advantage for a sometimes useful effect. This is a choice I'm not sure about and I may change it for something else after a few games.
Lightspawn for Leeroy Jenkins. It's a solid card, not quite the bomb that Leeroy is but it often functions as a full 5/5 or even better.
Stampeding Kodo for Abomination. Abom is intended to stall rush decks with lots of small creatures and the kodo does this too.
Gurubashi Berserker for Sylvanas. This card can be fantastic in priest decks because you can kill smaller things then heal it for a wildly escalating enrage bonus. I've seen these hit 17 attack in the arena. It synergies so well with the Priest class abillity, in fact it may even be a better pick than the legendary SpecialistSC chose.
Gelbin Mekkatorque for Argent Commander. Good solid creature with crazy inventions, some of which are really strong, especially if you have board control. Plus I don't know what all his inventions do and I like seeing new ones! You get this guy if you spend any money at all in Beta.
2 Sunwalkers for the Holy Fire and the Ragnaros. Very solid creature, it's a defensive version of the much admired Argent Commander.
Temple Enforcer for Ysera. Very powerful card with all sorts of synergies. It's great if it buffs the Lightspawn or the Berserker.
My guiding principle here was to go for the same mana cost (although I don't own anything good close to Ysera's mana cost) and, if possible, similar utility. When adapting a deck it's important to look for synergies and make sure you appreciate any combos you may be breaking. Fortunately here the cards I don't have are just strong cards but not particularly synergy cards, in fact the chargers possibly synergise worse with the priest's healing ability.
Here's the final deck I came up with. I made it to do my daily, 2 games later it's got 2 wins.The best moment was when the mind visions stole Ragnaros and Mind Control. He played Ragnaros, I played Ragnaros and it randomly blew up his Ragnaros. He then stole my Ragnaros and I used his Mind Control to take it back and kill him.