Priest leveling talents.

I have played priest for a long time and have leveled 2 priests to 60. With a careful selection of talents you can move from mob to mob with virtually no downtime whatsoever.

Discipline:
level - talent
10-14 - Wand Specialization 5/5

Wand spec is very good at low levels. Shield, dot and wand takes down mobs in no time at all with the extra 25% damage your wand.

Shadow:
level - talent
15-19 - Spirit Tap 5/5
20-21 - Improved Shadow Word: Pain 2/2
22-24 - Shadow Focus 3/5
25 - Mind Flay 1/1
26-27 - Improved Psychic Scream 2/2
28-29 - Shadow Focus 5/5
30-34 - Shadow Weaving 5/5
35 - Vampiric Embrace 1/1
36-38 - Shadow Reach 3/3
39 - Silence 1/1

Once you hit 40, go grab yourself a mount and head to your nearest priest trainer to get your talents reset. The higher level I became, the less I would use my wand. For this level, getting +10% shadow damage from the 'Darkness' talent, an extra +15% shadow damage dealt and -15% physical damage taken is much more important than +25% damage from wands.

Shadow:
Spirit Tap - Rank 5/5
Improved Shadow Word: Pain - Rank 2/2
Shadow Focus - Rank 3/5
Improved Psychic Scream - Rank 2/2
Improved Mind Blast - Rank 2/5
Mind Flay - Rank 1/1
Shadow Reach - Rank 3/3
Shadow Weaving - Rank 5/5
Silence - Rank 1/1
Vampiric Embrace - Rank 1/1
Darkness - Rank 5/5
Shadowform - Rank 1/1

Shadow:
41-42 - Improved Vampiric Embrace 2/2

Discipline:
level - talent
43-47 - Wand Specialization 5/5
48-49 - Improved Power Word: Fortitude 2/2
50-52 - Improved Power Word: Shield 3/3
53 - Inner Focus 1/1
54 - Martyrdom 1/2
55-57 - Meditation 3/3
58-60 - Mental Agility 3/5

After you hit level 60 it is then up to you how you want to spec your priest. There are many different possibilities of talent specs, many are listed here: http://forums.wow-europe.com/thread.html?topicId=12881515&sid=1

When leveling your priest try to get gear to improve you spirit, intellect and stamina. The more spirit you have the more mana you can regenerate from the 'Spirit Tap' talent. The more intelect you have the larger your mana pool. The more stamina you have the less squishy you are.