Resto Shaman's Meta Gems (patch 2.4.3)

Insightful Earthstorm Diamond: +12 Intellect & Chance to restore mana on spellcast

This should be every resto shamans' meta gem for their meta socket helm. The proc since patch 2.3 is 5% chance to restore 300 mana. When you have this, you can focus more on red healing gems such as Teardrop Crimson Spinel and spell haste gems such as Quick Lionseye instead of mp5 gems.

This meta gem also procs off water shield!

Mystical Skyfire Diamond: Chance to Increase Spell Cast Speed

It has a 15% chance to proc, and gives you 6 seconds of 320 spell haste rating. The hidden cooldown of this gem is 45 seconds. I wouldn't recommend this gem for healers because you don't always spam heal, and healing so fast along with other healers healing will usually end up with lots of overheals and drain your mana quick. There are times when you need to heal up the raid quick, but you might get stuck in the hidden cooldown for the gem to proc, so this isn't recommended.

Bracing Earthstorm Diamond: +26 Healing +9 Spell Damage and 2% Threat Reduction

The 2% threat reduction is not needed. If you need it, then something is wrong with your tanks, or you are just pulling aggro because you start healing like crazy in the beginning or you are pulling aggro from new add spawns. An earth shielded tank will pick up threat per second very quickly because the heals from the shield counts as if the tank was using healing spells on himself. You can socket your regular non-meta sockets with all the epic red healing gems you want.

You are not guaranteed to have a shadow priest in your group all the time. You also have to remember that downranking chain heals less than rank 4 receives downranking penalty.

So to sum things up: The Insightful Earthstorm Diamond is your best choice as a resto shaman.