There are two main schools of thought for Guardian tanking. One is a Hybrid Vigilance/Defense build with like a 24/17 split. Their reasoning is that the mid level Vigilance talents provide better bonuses than the upper tiers of defense. I don't subscribe to this school of thought, but if you are interested there is already a thread on it.
The second school of thought is a 34/7 Defense/Vigilance split. This is my preferred spec, and it does offer some flexibility in how you build it.
First off, a link to my build: http://www.torhead.com/skill-calc#500fMGcurroukZhMM.1
Talent Choices
Defense
Tier 1
TBH all the tier 1 Defense skills offer a lot to a tank build. You only need to take 5 points, but I think buying the whole tier is worth it.
Victory Rush- This talent is required as it helps make up the loss of focus we naturally incur using Soresu. Sundering Strike is your bread and butter focus builder. 'Nuff said.
Dust Storm- Adds a debuff to accuracy on Force Sweep. Useful, as a decrease in accuracy for an enemy means a gain in survivability for you.
Momentum- Free Blade Storm after Force Leap? Yes please, especially after the later talents that buff Blade Storm. This is probably the most optional of the T1 talents, but to progress you will have to put at least 1 point in it.
Tier 2- This tier seems to be a no brainer for a tank. 2 great tanking talents and a not so great talent.
Guard Stance- Mandatory. It increase your defense in your tanking stance
Lunge- IMO also Mandatory. Riposte is not on the GCD, and eventually with this spec it will give you defensive bonuses. Making it cost just one focus is a no brainer and you should be using Riposte in this spec every time it is up.
Solidified Force: Reduces the cost of our slow and Hilt Strike. Not worth the points as it does not increase our dps or survival. That said a nice pvp talent.
Tier 3: Again, mostly good, with one not so good talents, at least for our purposes.
Blade Baricade- Enhances Riposte to give you a defense bonus. With 3 points into it, that 6% defense for 6 seconds. This is why Riposte should be used whenever possible.
Warding Call- 40% damage reduction for 10 seconds. YES PLEASE!!!
Profound Resolution- More of a PVP talent. Reduce the cd on our cc breaker.
Pacification- Increase DPS for our 2 AOE's and Hilt Strike by 15%. Sign me up as an increase in damage is an increase in threat.
Tier 4- This is where those who advocate Vigilance/Defense Hybrids say the Defense Tree starts getting weak, I disagree,
Shield Specialization- Increase your shield chance, more avoidance equals more survivability.
Courage- Another optional talent. Useful in that it can reduce the costs of Sweep and Blade Storm, which due to their defensive buffs will pretty much be used whenever they are up.
Command- This is another semi-optional talent. Fully specc'd it reduces the CD on our AOE taunt and force push by 15 secs. I'll take that. More threat is always welcome
Tier 5- Solid Talents abound, nothing earth shattering, but solid.
Stasis Mastery- Makes Force Stasis instant rather than channeled. Handy considering it's one of our only cc's
Hilt Strike- Optional. Hilt Strike would be much better if the cd wasn't a minute. Still a handy ability. High threat is always nice, as is the stun.
Force Clap- Adds a 2 second stun to Force Leap. Again, more of a pvp talent. Optional.
Blade Barricade- Adds a damage shield to Blade Storm. Quite handy.
Tier 6- Gravy. Both talents here are worthwhile.
Cyclonic Strikes- Improves Soresu Stance's focus generation and using Cyclonic Slash reduces the cd on Combat Focus, which gives us free focus. Mandatory
Inner Peace- I'm torn on this talen as it reduce the cd on Enure (meh) but increase elemental and internal damage resists (yes). This talent comes down to your preference.
Tier 7- Guardian Slash- YES. DPS central. While the hybrid crew will point out Vigilance puts out more dps, Guardian Slash makes sense in that you should be able to keep five stacks of Sunder up for it to do it's max damage. More Damage more threat.
Vigilance Tier 1
Improved Sunder- Makes Sunder stack twice instead of once. Mandatory.
Swelling Winds- 30% more damage and a reduced cd on one of our 2 AOE's. Yes especially With Dust Storm.
Single Saber Mastery- Meh, better for the DPS and pvp, doesn't help since we tank in Soresu.
Vigilance Tier 2
Defiance- More of a pvp skill.
Perseverance- Gives us strength, which in turn gives us damage, which in turn gives threat. Very Nice
Accuracy- Increase our Accuracy. Also important as if we don't hit, we don't do damage. If we don't do damage, we don't build threat. This is really a toss up between Perseverance in my build. But if you ditch some of the optionals in defense this is a good home.
Just my 2 credits.