DPS (Non-epic) Caster Gems

It's exciting to get a new piece of gear, but when it has sockets, I've always found it a little daunting as well, feeling like I wasn't really familiar with what options are out there. Here's a list and mini-guide to socketing for dps caster types. The list of gems is at the bottom and doesn't include any epic quality gems, because they are REALLY expensive, and you need to really make an informed decision when you're socketing a piece with that. I also tend not to use them because most of my pieces are epic quality on their own. My rule is you should only really put as good a quality gem in a piece as that piece's quality. So, if you have some blue pantalones, don't go socketing an epic purple gem... save that for your epic head piece and throw a bluey in the pants.

Color Categories and Characteristics
First let's look at the colors of gems and what generally characterizes those colors so you know what your general options are before you start looking at all the individual gems. There are first, the three socket colors: red, blue and yellow.

Red = + damage, at various levels, but always pure damage.
Blue = spell penetration or stamina.
Yellow = spell stats (like hit or haste), resilience, int, and NOT DAMAGE

A lot of pieces have a combination of red and yellow slots so you can add a damage gem and a non-damage gem. But of course, you have other options as well in the not so primary colors of gems to socket:

Purple fits inbetween red and blue, blending the spell damage and stamina. (No spell penetration).

Orange blends red and yellow, giving you the red damage with yellow spell stats, (like crit and hit).

Green gives you the blue stam or penetration and the yellow spell stats.

The primary gems give you the most quantity of the stat they influence, but of course, the blended gems give you increases in multiple categories with the sacrifice in the amount those stats get buffed.

The best way to figure out where you want to be in terms of socketing is by looking at where you'd like your stats to be. If you are pretty much there in all categories, go with the blended gems because they'll increase more of your stats evenly. If you are seriously lacking in an important stat, like resilience when first getting into pvp, you might want to socket primary gems to give you the most bang for your buck in terms of catchup.

Meta gems are sort of on their own and tend to require more gems of the type of stats that they supply. There are also some interesting possibilities in terms of cast time, mana cost, etc. with the metas. You should look at the list and see which ones interest you the most. All the ones I've listed below would make good caster gems, so you need to decide what stats are going to benefit your playstyle and character the most.

Caster Gems
Here's a list of relevant gems for caster types of uncommon and rare quality:

Red - Runed Living Ruby (+9 Spell Dmg)
Red - Runed Blood Garnet (+7 Spell Dmg)

Purple(R/B) - Glowing Nightseye (+5 Spell Dmg, +6 Stam)
Purple(R/B) - Glowing Shadow Draenite (+4 Spell Dmg, +4 Stam)

Blue - Stormy Star of Elune (+10 Spell Pen)
Blue - Eye of the Sea (+15 Stam)
Blue - Solid Azure Moonstone (+9 Stam)
Blue - Stormy Azure Moonstone (+8 Spell Pen)

Green(Y/B) - Dazzling Talasite (+4 Int, +2 mp5)
Green(Y/B) - Forceful Talasite (+4 Spell Haste, +6 Stam)
Green(Y/B) - Notched Deep Peridot (+3 Stam, +4 Spell Crit)
Green(Y/B) - Radiant Talasite (+4 Spell Crit, +5 Spell Pen)
Green(Y/B) - Steady Talasite (+4 Resil, +6 Stam)
Green(Y/B) - Unstable Talasite (+4 Stam, +4 Spell Crit)
Green(Y/B) - Dazzling Deep Peridot (+1 mp5, +3 Int)
Green(Y/B) - Radiant Deep Peridot (+3 Spell Crit, +4 Spell Pen)
Green(Y/B) - Unstable Peridot (+4 Int, +6 Stam)

Yellow - Brilliant Dawnstone (+8 Intel)
Yellow - Gleaming Dawnstone (+8 Spell Crit)
Yellow - Great Dawnstone (+8 Spell Hit)
Yellow - Mystic Dawnstone (+8 Resil)
Yellow - Quick Dawnstone (+8 Spell Haste)
Yellow - Brilliant Golden Draenite (+6 Intel)
Yellow - Gleaming Golden Draenite (+6 Spell Crit)
Yellow - Great Golden Draenite (+6 Spell Hit)

Orange(R/Y) - Potent Noble Topaz (+4 Spell Crit, +5 Spell Dmg)
Orange(R/Y) - Reckless Noble Topaz (+4 Spell Haste, +5 Spell Dmg)
Orange(R/Y) - Unstable Topaz (+5 Spell Dmg, +4 Int)
Orange(R/Y) - Veiled Noble Topaz (+4 Spell Hit, +5 Spell Dmg)
Orange(R/Y) - Potent Flame Spessarite (+3 Spell Crit, +4 Spell Dmg)
Orange(R/Y) - Veiled Flame Spessarite (+3 Spell Hit, +4 Spell Dmg)

Meta - Chaotic Skyfire Diamond (+12 Spell Crit, +3% Crit Dmg)
Meta - Destructive Skyfire Diamond (+14 Spell Crit, +1% Spell Reflect)
Meta - Ember Skyfire Diamond (+14 Spell Dmg, +2% Int)
Meta - Imbued Unstable Diamond (+14 Spell Dmg, +5% Stun Resist)
Meta - Insightful Earthstorm Diamond (+12 Int, Chance to restore mana on spellcast)
Meta - Mystical Skyfire Diamond (Chance to increase spell cast speed)
Meta - Powerful Earthstorm Diamond (+18 Stam, +5% Stun Resist)
Meta - Swift Starfire Diamond (+12 Spell Dmg, Minor run speed increase)