Arcane Tree

Probly best to start with the Tree itself. Currently the basic tree is 57/3/11 (something like this).

The arcane tree runs out of DPS improving talents very quickly so its better to get them from other tree. It is a shame that the utility talents aren't very useful. There are few points that can spend to customise the spec, but they will change the playstyle of the spec. So lets have a look starting with Fire since we have 3 points in it

Fire

Tier 1
3 pts Incineration: +6% Critical Strike chane on Arcane Blast.

Frost
The whole point of points in frost is to get Icy Veins.

Tier 1
3 pts Ice Floes: lowers cooldown on Icy Viens, Frost Nova and Ice Block
2 pts Frostbite: Just as you have to use the points and its more useful here. Provides some benifit to grinding as I find the best rotation for this is FFB, AB, ABar

Tier 2
3 pts Precision: +3% hit will all spells, -3% base spell mana cost.
2 pts Ice Shards: +66% damage on critical strike. For when AoE is needed or FFB is used

Tier 3
1 pt Icy Veins: Lowers cast speed by 20% and reduces pushback for 20 seconds (cooldown 3 minutes/2 minutes 24 seconds with 3 points in Ice Floes).

Arcane
You will find from the ones I put x pts that you will need to go back and choice some of these as you will need 5 points per tier to move onto bying the next level of Talents.

Tier 1
2 pts Arcane Sublety: Reduces threat from Arcane spells by 40%
3 pts Arcane Focus: +3% hit with Arcane spells, -3% base spell mana cost of Arcane spells
x pts Arcane Stability: This one is personal choice, but pushback from being attacked really blows and this is one way of dealing with it- most people take three points and enjoy the pally -35% pushback buff.

Tier 2
0 pts Arcane Fortitude: this is not a PvE talent
x pts Magic Absorbtion: This increases resistance and when a spelll is fully resisted gives back mana. a very nice general talent.
5 pts Arcane Concentration: 10% chance after a spell hits of going into a clear casting state and the mana cost of the next spell cast reduced to 0. Not as tasty as it used to be (AB is now +175% rather than 200%), but still considered core. Due to is placement on the tree I think it would be difficult to not buy this talent and use the points effectively. To make up for this it recieves a benifit from Arcane Potency (Tier 6) for an additional critical strike chance

Tier 3
x pts Magic Attunement: Increases range of Arcane spells (x3 yards). while it doesnt' increase DPS in WotLK it has meant that you can be out of the range of AoE that various bosses do meaning it enables you to continue DPSing uninterupted.
3 pts Spell Impact: +6% damage Arcane Blast. This is massive, in terms of pure casting your going to be casting AB 80% of the time or more.
x pts Student of the Mind: up to +10% spirit. not really desirable until T8/9 equipment when used in conjunction with Molten Armour for additional crit. With Arcane don't really desiring crit it can be a nice boost, but will come at a cost of sacrificing a DPS talent elsewhere. This is not currently considered an optimal talent.
1 pt Focus Magic: Gives a buff to another player for 30 minutes of +3% spell critical strike, however when they crit you get +3% critical strike for 10 seconds.

Tier 4
x pts Arcane Shielding: Lowers mana cost of Mana Shield and increases resistances on Mage Armor. IF your using Mage Armour... it can be great for some additional resistances and should be used in conjuction with Magic Absorbtion.
0 pts Improved Counterspell: although I have put 0 here it could be taken but most bosses are immune to counterspell.
3pts Arcane Meditation: +50% mana regeneration during combat.
3pts Torment the Weak: +12% damage to snared or slowed targets. All tanks apply this in one way or another so its a core talent.

Tier 5
0 pts Improved Blink: While sexy is just not a PvE talent
1 pt Presence of Mind: instantly cast a spell with a cast time less than 10 seconds. A great DPS boost and recieves a bonus critical strike modifier from Arcane Potency (Tier 6).
5 pts Arcane Mind: increases intellect by 15%, +mana, +crit. very sexy but limited.

Tier 6
0 pts Primatic Cloak: Again very sexy but isn't a PvE talent
3 pts Arcane Instability: +3% critical spell strike and +3% damage all spells
2 pts Arcane Potency: +30% on your the spell benifiting from either PoM or CC

Tier 7
3 pts Arcane Empowerment: Gold increased damage of your main nukes AB & AM
1 pt Arcane Power: For the next 15 seonds all spells cost +20% mana but does +20% more damage
0 pts Incanter's Absorption: Sexy, but too situational for real benifit. Arguable would work well in fights that do constant damage or use frost/fire ward, as the use of Mana shield would be to expensive.

Tier 8
2 pts Arcane Flows: Lowers cooldowns PoM, AP and Evocation. Gold!
5 pts Mind Mastery: turns 15% of intellect into spellpower.

Tier 8
0 pts Slow: Very sexy for soloing but not so for raiding.
5 pts Missile Barrage: This is it... the bees knees of Arcane this is a huge DPS boost.

Tier 9
3 pts Netherwind Presnce: +6% haste = +6% DPS
2 pts Spell Power: +50% (a for a total fo +100%) damage on a critical strike of all spells

Tier 10
1 pt Arcane Barrage: Arcane only instant spell. Not so sexy at the moment, but very useful and no doubt will be back into the rotation after 3.2.2