Well, this post is for you, aspiring PVP laserchicken.
Gems:
I actually struggled with this myself for a while. Is it better to gem flat resil, flat spellpower, flat spell pen, flat stamina, what? In my opinion, one is better off gemming for spellpower and spellpower/resilience, particularly once your gear set is almost complete. Personally, I have a combination of resil, spellpower, and spellpower/resil WITH ONLY ONE gem that happens to be spellpower/stamina, and that was used to push me over a certain HP milestone which I can't remember right this second.
You can leave a couple blue gem sockets open (better blue for the socket bonus, tbh, to help get back stats you miss) to gem spell penetration.
What *is* spell penetration, you ask? And how much of it do I need?
Spell penetration on WoWWiki
In PvP, good spell penetration values are 54 (to counter unimproved Mark of the Wild, 75 if the druid spent two points in Improved Mark of the Wild) and 130 (to counter various single-school resistance buffs, such as the Paladin's resistance auras); these are usually enough. 50 will often do for 'occasional' PvP.
As the article states, every point of spell penetration counteracts a point of resistance. 50 is a solid minimum if you don't expect to PVP much, or if you only PVP casually. Something between 75 and 130 seems to be more reasonable if you do arenas. I personally have been skimping out on gemming/enchanting spell pen because I'm going to be getting some upgrades soon, and I'm a cheapass. But I have 40 spell pen right now, and that is actually a noticeable difference.
So in summary:
* spellpower or spellpower/resil are solid gems
* gem flat resil only if you feel you're behind on anti-squishiness
* save a couple blue sockets for spell penetration
META!
Before you go coughing up dough for some of these meta options, swing by your local Wintergrasp and get them for stone keeper's shards instead. You're welcome.
There are many many options, and frankly...most of them are great depending on what you centrally do in PVP. I personally use the Forlorn Starflare Diamond, as keeping me silenced is a bad idea. I got this gem specifically because I do a lot of arenas. In 2v2, if I get silenced, my partner is in critical danger. If I were exclusively doing BGs, or only 5s, I imagine I would get Tireless Starflare Diamond instead for the run increase.
There are gems there that increase your crit and add these wonderful things, but I find foremost that the spellpower is lacking in a lot of PVP gear. I am aiming to bring my spellpower back up to about 2900-3000 in caster form before I switch my meta. When I do, I'm going to probably switch it to Impassive Starflare Diamond for the crit and reduced fear duration.
Bear in mind that most of my specs listed in this post do not include eclipse, our primary reason to stack crit. Food for thought!
Your mileage, as always, may vary. There are quite a few options here as opposed to PVE (Chaotic Skyflare Diamond or bust), so play around, see what works for you.
I don't want to bog you down with information, so enchants will come in another post. Coming up: enchants, and links I like.
