Resistance effects and values @ 85:
Mage Armor: 45 (confirm?)
Mark of the Wild (Druid): 136
Blessing of Kings (Paladin): 136
Elemental Resist Totem (does not affect shadow) (Shaman): 195
Shadow Protection (Priest): 195
Resistance Aura (Paladin): 195
There are also racial (Undead, Draenei, Worgen etc.) effects that now give +85 Shadow Resist @level 85 instead of -% chance to be hit. Apparently these don't stack with the resist buffs anymore; for example, an Undead with Shadow Protection will still only have 195 Shadow Resist instead of 280. So extra pen/hit won't be necessary for these anymore.
Spell hit: 4%, racial penalties are gone and so is the +hit talent we used to have in 3.0, so with 102.5 hit rating for 1% spell hit at 85 (that's the value I found at EJ), you should be aiming for 410 hit rating unless all your friends are Draenei.
Curse of elements reduces resistances by 183 at 85, so you can basically rely on keeping that up for the majority of Spell Penetration needs, but with the buggy way Jinx works and the value of the utility curses (CoEx/CoW/CoT) I think I will prefer gemming the Spell Pen on my gear for the time being. If you'd prefer to rely on CoE alone, read no further. Also, I think the Mage Armor bonus is now minor enough that the main goal should just be 195.
There's 2 PvP gear slots that give Pen as an off-set stat, Neck and Back:
http://www.wowhead.com/item=64808 178 SPen (Bloodthirsty)
http://www.wowhead.com/item=60661 201 SPen (Vicious)
http://www.wowhead.com/item=64732 178 SPen (Bloodthirsty)
http://www.wowhead.com/item=60786 201 SPen (Vicious)
The Neck slot's alternative stat is Haste (119 rating on Bloodthirsty, 134 on Vicious).
The Cloak slot's alternative stat is Mastery (119 rating on Bloodthirsty, 134 on Vicious).
Spell Pen Gems:
Stormy Chimera's Eye +84 Spell Pen
Stormy Ocean Sapphire +50 Spell Pen
In 4.0.6 there will be 20 Pen/20 Resil hybrid gems (http://ptr.wowhead.com/item=68741), hopefully it will be 25 Pen when released since that's probably a bug.
Spell Pen Enchants:
+70 SPen to cloak (http://db.mmo-champi...spell-piercing/)
this is an alternative to +50 Int to cloak (http://www.wowhead.com/spell=74240)
The Spell Pen cloak enchant value seems to be inflated as always, since it has 40% more (70/50 = 1.4) than the Intellect cloak enchant despite it only being 25% cheaper (50/40 = 1.25) on gems budget.
Spell Hit (Bloodthirsty):
119 Hit from Ring
138 Hit from Gloves
138 Hit from Belt (Alternative option: 138 Crit)
119 Hit from Wrists (Alternative option: 119 Mastery)
I'd value Crit as still fairly low for Affliction, so I'd say the best setup would probably be the Hit Belt, which would put you at 138+138+119 = 395 Hit Rating, only 15 Rating short of the 410 cap. The remainder can be obtained with a 20 Haste/Int +20 Hit gem, which also fills a blue socket.
Spell Hit (Vicious):
These alternatives may or may not exist, datamining is weird for Vicious, so I'll refrain from saying anything until it's all live:
134 Hit from Ring
159 Hit from Gloves
159 Hit from Belt (Alternative option: 159 Crit, Mastery, Haste)
134 Hit from Wrists (Alternative option: 134 Mastery, Crit)
134 Hit from Neck (Alternative options: 134 Haste, 201 Spell Pen)
159 Hit from Boots (Alternative options: 159 Haste, Crit, Mastery)
Keep in mind that using full PvP gear gives you, by my count, 3 Red, 3 Yellow, 3 Blue, 1 Meta, 1 Prismatic sockets (http://www.wowhead.c...=80;crs=7;crv=0). The Blue ones can be matched with either Hit, SPen, or Stam, and it's very likely you'll want to match most sockets on the S9 gear because the bonuses are very good.
Option 1: +50 Int Cloak Enchant, Bloodthirsty Neck/Cloak SPen offset items + 25Pen/20x gem (Puts you at 203, 8 over cap) or Vicious Neck/Cloak.
Option 2: +70 SPen Cloak Enchant, +84 Prismatic gem, +50 Spen gem puts you at 204, 9 over cap.
Option 3: +70 Spen Cloak Enchant, 2 +50 Spen Gems, 1 +25Spen/20 resil (Vivid Dream Emerald) gem puts you at exactly 195.
Summary (i.e. what I think I'm going to do): I'll probably be wearing more or less full PvP gear for the early part of the season, going with the Haste Neck, Mastery Cloak, Hit Belt and Mastery Wrists. I'll be using the Spen Cloak Enchant option to take advantage of the inflated budget, and then filling my 3 blue Sockets with 1 +84 Pen gem (the Prismatic Spell Pen gem is very slightly inflated budget-wise as well, 84 instead of 83.75, bigtime gain there...), 1 +50 Pen gem, and 1 20Haste/20 Hit gem, to maximize getting useful (i.e. non-Stamina) value out of the blue sockets.
Update: The lack of 25Pen/20x hybrid gems definitely changes the optimal gearing solutions. I think the best solution now is to just get the Vicious Spell Pen cloak with +50 Int enchant for all spell pen. Then use either Veiled Demonseye (http://www.wowhead.com/item=52217) or Lightning Dream Emerald (http://www.wowhead.com/item=52225) for your 3 blue sockets, and reforge out of hit as some have suggested to get back to 4% hit. You'd probably reforge either Ring or Wrists if in full Bloodthirsty, and either Belt or Gloves if in full Vicious.