Insightful Earthsiege Diamond
The Insightful Earthsiege Diamond is a good chunk of Intellect (increase of mana pool size and spell crit) and has a chance to restore mana with every spell cast. It requires one gem of every color, making it an easy meta to fill the requirements of. One Nightmare Tear/Enchanted Tear/Enchanted Pearl can completely fulfill all the requirements. The above gems may not be the best choices to fulfill your needed colors, but if you have no other gem slots besides your helm and its extra slot, you can still have a good meta with a decent bonus. Otherwise, a purple and orange are often good bets.
There has been some debate as to the effectiveness of this meta. But this was before Druids were throwing out Rejuvenations left, right and center. With a lot of casting, a larger mana pool is extremely helpful, and that extra bit of crit will come in handy with 4-piece T9. As well, the constant casting gives the Mana Restore more chances to proc during any fight. This makes it a very versatile meta, one focused more on longevity than pure power. Keeva talks more about this and the next meta on her site here.
Ember Skyflare Diamond
This is the "powerhouse" meta, and the most commonly utilized by Restoration Druids at end-game where mana regen is less of an issue. It has requirements that mean you must have three non-meta gem slots available to you, as it needs three red gems to activate (no combinations to grab two requirements at once). However, this is no detriment as far as Restoration Druids are concerned. Our four best gems all fill red requirements (Spellpower, Spellpower/Spirit, Spellpower/Haste, Spellpower/Intellect). If you have the gem slots and you want a boost to your straight-up healing numbers, this is the meta for you.
Spellpower is KING for Restoration Druids, no ifs, ands or buts. This straight up gives you 25 spellpower and 2% more Intellect. The Intellect gain is not off your base, it is off your current Intellect number, bonuses and all. That means it scales with gear as well as buffs. With it giving a larger mana pool and more crit, this meta is much more efficient, so long as you were not relying on your meta to recover your mana and you have the available gem slots.
There's no mistaking this choice; if you're going red, you're going Runed. Restoration Druids love Spellpower. It's our bread and butter. This is the single-most commonly used type of gem in our gear, for good reason. If you have a red slot, there is no doubt what should go into it.
Runed Dragon's Eye (Jewelcrafter only)
Runed Cardinal Ruby
Runed Stormjewel (Fishing Daily reward)
Runed Scarlet Ruby
Perfect Runed Bloodstone
When it's time to go mixed gems, the Purple gem is your best friend. Purified gems have both Spellpower and Spirit, so if it's time to fulfill the requirements for your IED, or you're looking at a nice set bonus, or you're in need of some regen, grab some Purified gems.
Purified Twilight Opal
Perfect Purified Shadow Crystal
Purified Shadow Crystal
Orange has two great options for Restoration Druids: Spellpower/Intellect or Spellpower/Haste. What you pick depends entirely upon your needs. Is your haste below 300? Then you want something Reckless. Is your mana pool a bit low but your Haste is fine? Go for Luminous!
Reckless Monarch Topaz
Perfect Reckless Huge Citrine
Reckless Huge Citrine
Luminous Monarch Topaz
Perfect Luminous Huge Citrine
Luminous Huge Citrine
How Do I Gem My Gear?
You got me.
Haha, no, seriously, gemming gear may be a little less complicated for a Resto Druid than other classes (I have had to regem Bellbell's melee gear three times in one day, and she's not even as complicated as some others!), you can still mess it up if you don't keep a lot of different things in mind. And by "mess it up" I mean "you might be missing out on some benefits but it probably won't kill you unless you try to apply to a top guild because they take gemming seriously."
Gemming for Spellpower Bonuses
On some gear, there will be a bonus for aligning your gem colors properly to gain a set bonus. Generally, you can ignore this. But if the bonus is for Spellpower, it is time to start weighing your options and thinking. Generally, no gemming bonus will match raw Spellpower gems. However, if you are missing one of the previously mentioned stats (Spirit, Intellect, Haste), then the sacrifice of a few points of Spellpower to give those a little boost is not a bad choice. This method requires good judgment, however, as overgemming your Spirit can become a waste, and eventually your gear can reach a point where you have too much regen and it is wasted (this is a case-by-case scenario and really requires a lot of personal testing, as well as knowledge of the requirements of different encounters and your own role in those encounters).
Gemming Straight Spellpower
This is the fall-back of a lot of Druids because, well, it's easy and it works. Restoration Druids benefit a lot from Spellpower. We just eat it up, and it helps that one of our two best metas needs three red gems. The only downside to this is sometimes missing out on gem bonuses, but if you have the mana regen to allow for straight Spellpower gemming, you're not too concerned with adding some Spirit or Intellect here and there. And, since you would only be gemming for Spellpower set bonuses anyway, it's more effective to ignore it since all you want is Spellpower, and losing a few points over something else isn't worth it. This is the general gemming style of the JC Restoration Druid simply because of the huge amounts of Spellpower they gain from their special gems.
It's possible to do both methods with a prudent application of judgment. I am currently in this practice, as I have sometimes chosen some Spellpower bonuses in favor of a little extra Spirit, but my newest pieces have been gemmed for raw Spellpower, bonuses be damned. My regen has reached the point that, so long as I use my innervate responsibly, I have no reason to gem for more regen (unlike a certain Holy Paladin who constantly asks for Feral innervates). Like everything with a Restoration Druid, it's understanding your balance of stats. And once they're balanced, it's time to overload the scale with Spellpower!
What Level of Gems Should I Use on My Gear?
Now that we have the full complement of uncommon, rare and epic gems, how do you know when it's time to upgrade to the next level? When is the cost appropriate? Well, some of it is obviously up to your current monetary/profession situation, the demands of the guild you're in and personal preference. A general guideline to follow is:
Quest Greens and Low-level Blues -> Uncommon Gems (non-perfect)This is, of course, just a rough guideline and you should use your best judgment when it comes to what you can afford and what you need. Epic gems are not the cheapest, and if you still need your Emblems for buying gear, then it may be more prudent to wait until your 226 iLevel gear to start using them.
High iLevel Blues -> Uncommon Gems (perfect)
iLevel 200-213 Epics -> Rare Gems
iLevel 219 and beyond Epics -> Epic Gems
I know it was a lot to read through, but I hope it was helpful. If you ever need personal help with gemming and you'd like to trust the help of some random Resto on the internet, feel free to e-mail me!