Ok, I've recently started to use Taric a lot in 3v3. Why? Besically because there often isn't a tank on your team, and because Taric is great at what he does. He's got an amazing stun, a great heal, and with his passive he can stay in the lane for a very long time.

The first build is for going against AP heavy teams, and the second one for AD heavy teams. If the enemy team lacks CC, you can get Boots of Swiftness instead.

Both builds are basically the same, just with variation of purchase order, and boots.

Pros
Tanky
Great stun
Great Heal
W passive is an Armour Aura
Amazing AD buff for nearby teammates
Ult is also a healing Aura
Can stay in lane for a long time
Can, I repeat, CAN Backdoor a tower with an AD carry and your ult after Zhonya's. (so fun to do :D)
He's just totally Fabulous!!!

Cons
Hard to run away from more than one opponent.
Hard to get enough gold.
With some hard CC, he can be brought down, especially if he can't heal
Might be too fabulous for some.

Mage Pen. reds for greater damage with your W and E
Mp5 per level blues and yellow for better lane staying power
Flat health quints for that early game gank advantage. 78 health does a lot

I go 9-21-0 tanky caster masteries taking Exhaust in Offence and anything to increase your tankiness in defense.
The extra 48 from defense masteries works nicely with your quints for a whopping 126 extra health at start, before your extra 100 health from Doran's ring.
Taric should start out with almost 700 health and 2 escape/chasing summoner's spells and a stun. It'll really help out your team getting that oh so important first blood.

Gemcraft (Passive)
While you should be trying to let your laning partner get most of the last hits, it's a good idea to attack minions just to get the extra mana regen from your passive.

Imbue (Q)
Remember, this ability heals both yourself and your target. This can also be cast on your minions. It may seem dumb to do, but if you see yourself with some health missing, and enough mana, why not heal a minion too?

Shatter (W)
This is going to give you most of your minion kills. It has a pretty nice range on it. Hovering over the ability in game will reveal that range. After stunning an opponent, walking up to them and casting Shatter is a great harassment technique. It will also not pick up minion aggro.

Dazzle (E)
Your bread and butter ability. Stunning is your major role as Taric. Stun for your teammates, stun for your tower, stun for fun. Just STUN!!!!

Radiance (E)
Ahh, the sweet, low CD, high Mana cost spell. This turns Taric into a Tanky AD champ giving you +90 AD, and it hands a shiny B.F. Sword to your nearby allies. This ability makes me love teaming with 2 AD carries, like Xin Zhao and Tryndamere. Also, this buff affects minions as well. So... It's like 6-7 BF swords per minion wave :D

Always start out with Doran's ring. The 15 extra AP, bonus health and Mp5 are exactly what Taric needs.

If you get first blood before minion spawn, be sure to go back for your boots and a health pot.

When you hit 600 gold, , and you feel it's safe, get your Boots and an Elixir of Brilliance if you don't already have the boots. If you do, just wait until you can afford to finish upgrading the boots to get the Elixir.

Elixirs are very important in 3v3. They give a great buff for their very low cost. 3v3 is all about getting the most bang for your gold.

It's time to start building your Chalice of Harmony. This item is so very important. It's only 890 coins and will keep you from going out of mana of long for the rest of the match. This is very important because you're always going to want to be healing something, or stunning someone. It'll also keep your Radiance running longer, which is always good.

Next start building your Abyssal Mask or your Zhonya's Hourglass. If you're doing well, and don't feel like your enemy team is causing a big threat, you can start getting the offensive item first.

After building your Abyssal Mask and your Zhonya's Hourglass the game is probably already been decided, and you're probably winning. If you're not winning, then you're probably still working on your second of these two, or worse yet the first. You should probably surrender, or just pray one of the opponents disconnects.

If you're still playing at this point, start working on your Rabadon's Deathcap. This item is going to boost your AP a lot, and it's going to cause your Dazzle and Shatter to do some crazy damage. Remember Dazzle does more damage the closer you are. It doesn't matter where you cast it from, but where you are when it lands.

Nashor's Tooth is really nice for your passive, giving you that extra mana whenever you need it, and it works so well with your ulti. Feel free to place this wherever you want.

Flash This is your best way at getting away from anyone chasing you. Stun, and cast this. You're almost always close to the jungle, so Flashing over a wall is your best bet.

Exhaust works very well with your stun. Your enemy is getting away from one of your teammates. Cast your stun, then walk up and exhaust. Then laugh as their health melts away.

Clairvoyance is always a nice summoner spell to have. The low CD lets you see where their jungler might be if they have one, or if they're at Dragon or Lizard buff. If you take this, be sure to cast it at the beginning in the bottom bush. It's so much better than having a teammate, or yourself facecheck it only to find 3 angry opponents with clubs and swords clobbering you or your teammate down.

Heal No real need for this spell since at level 2, you're going to be able to heal both your laning partner and yourself at the same time

Clarity No... just no... Your passive is like a Clarity over time, and once you get your Chalice of Harmony, you'll only be using it to give your teammates mana.