My main will likely be a Templar healer, but I also plan to have a tanking spec. I like the wide range of abilities available to that class, which should make for a versatile tank. The main bar will probably look like this:
http://www.esohead.com/calculator/skills#zoaXRj28bOx8RjI8RGb8kNw8kjQ8N7JLDM6LDi6rDu6zDG6LDT6MbMUf6MbMXO8T7JLRMA6MrqAi6MrqAI6MrqAD6crqLw8j7DrSZ6zUM6rUR6MrJO16MrJPr6MrJPu8n7JLWF6zWQ6LWZ8y7HLR3r6rR3f6MfQE16MfQE36MfQlu6MfQlI8P7mLdYf837zrw3Y8zM7pcgcmM6cgcmm6zgcoS6cgkvQ
Luminous Shards: Helps with both magicka and stamina regen for you and one other group mate, and also should help hold AoE aggro.
Blazing Shield: Damage prevention for you as well as more AoE damage/aggro generation, both on activation and also when the shield runs out.
Purifying Light: Debuff that helps your group deal damage. Hopefully, you get credit for the additional ~33% damage (huge threat generation if that's true.)
Restoring Focus: Defensive buff and increased healing for both you and your group. Replace with Unstoppable if you already have a Templar in the group using this ability.
Pierce Armor: A true taunt, and another debuff to the target, again increasing the damage of your group. I see this as a must-have for tanks, way better than the Dauntless taunt IMO.
Solar Prison (Ultimate): Enemies deal less damage, combined with a stun effect synergy? And it's AoE? Yes, please.
This build offers a nice balance of buffs for you and your group, offensive/defensive debuffs to the enemy, plenty of AoE threat generation (as well as the single-target taunt), and to top it off has a little bit of regen from Luminous Shards. My second hotbar would probably be full of long-duration healing ground effects (Sanguine Altar, Extended Ritual, Ring of Preservation, etc.) Those are all things I can lay down when the opportunity presents itself, then forget about for 15-20 seconds. Add in Binding Javelin and a leap attack of some kind (Shielded Assault or Toppling Charge) for PvP, and I think this will be an effective tanking build for most situations.
-Travail.