Taric is a support tank.

Taric is a versatile character who will benefit from a large number of stats. Taric needs mana and mana regen in the early game, but the need for mana is dealt with by utilizing attack damage and attack power as the game progresses ( Gemcraft). Cooldown reduction is useful on Taric, but attack speed becomes cooldown reduction on your heal. Armor penetration, stacked onto Taric's Shatter, complements the build as well. This build accommodates Taric's need for mana regen without excess risk early in the game, his need for mobility as lane dominance is tested mid-game, and his need for attack damage, armor penetration, attack speed and mana to finish the game off. Mana might seem like an odd choice, but the mana on a Manamune is enough to trivialize the rising cost of Radiance long enough for it to be useful without excessively draining your mana.

I use Clairvoyance for map awareness. AD Taric is a sub-par support character, but that doesn't mean that you shouldn't prevent ganks.

Exhaust is a useful spell to have as AD Taric, as it keeps enemies from running away and reduces their armor (through Cripple).

If you don't like one of the above options, Clarity helps with your ultimate and the sustainability of your lane partner.

These are the most common choices. If you feel a different summoner spell can be used as effectively, feel free to say so in your comment. I'll be happy to add it to the guide.

My mastery options might seem really, really odd. However, because Taric is not a cookie-cutter AD character, you'll have to use your masteries to help him stay relatively competitive.

Offensive Tree:
Deadliness : Everyone loves crit chance.
Cripple: This turns your Exhaust into a serious disable.
Alacrity : Everyone loves attack speed.
Sunder : Combined with possible rune choices and Shatter, you won't really need armor penetration.

Defensive Tree:
Hardiness / Resistance : To keep you alive.
Strength of Spirit : Considering the mana you'll have late-game, this is serious regen.

Utility Tree:
Good Hands : Name me a game you didn't die, or when coming back more quickly wouldn't have helped.
Expanded Mind : More mana is more Manamune and more Radiance.
Utility Master: When no one else take buffs, take them yourself. Both buffs help Taric immensely.

A lot of these runes are used to augment Taric's early-game. Marks are armor penetration, being the most significant increase in DPS next to Taric's W ability (though attack speed can be a viable alternative, considering the fine print on Taric's heal). Seals are flat mana regen, to assist with Taric's heavy mana usage early- to mid-game. Glyphs are of max mana per level, to provide attack damage and longer ultimate at the end of the game. Alternative glyphs include flat ability power for greater early-game heals, cooldown reduction per level for more buttons to press late-game, and more flat mp5. Quintessences can be whatever you like. I choose armor penetration, but I've seen attack speed, flat health, flat mp5, cooldown reduction per level, etc.

We start out with an item for mana regeneration, to let us use our high-cost spells aggressively. Boots are very important in laning, and come next. If you find the AS boots lackluster, Boots of Mobility, Boots of Swiftness and Mercury's Treads are all great options. Attack speed, attack damage and sustainable mana are chosen next, followed by a heavy slow with survivability and then your big, expensive weapons. I generally choose the Bloodthirster, because I love the lifesteal as my heal becomes less delightful, I need to start stacking its effect, and because it's cheaper. I welcome alternative items in the comments.