Post 2.3, a serious suggestion and 2 silly ones.
My current "default" spec:
http://www.wowhead.com/?talent=sZV0tIx0dMgqtVbx0h
Highlights:
-The Standards. If it reliably increases survivability, it's in here. Nuff said.
-Great spell damage reduction. The synnergy of Spell Warding and Pursuit of Justice results in a 7% overall reduction (4% reduction, 3% avoidance) of incoming spell damage.
-Mobility. Paladin tanks *were* the least mobile of the tank classes, lacking a charge. This was offset with ranged threat and taunt abilities. PoJ lets us have the best of both worlds: 15% run speed boost (independant of gem/enchants) is almost an "always on" intercept. It takes a little adjustment, but the positional control afforded by this talent is nothing to sneeze at.
-No Reckoning. I miss it when I'm soloing or overmitigating. On that big, bad, slow-swinging boss, though, I do NOT miss the occasional Reckoning-inspired Parry bursts. Ahhh, Reckoning.... 10% chance to buff the swing timer of a raid boss.
My "5-man healers are getting bored so I'm spamming JoB" spec:
http://www.wowhead.com/?talent=sZVothx0zxgoZVfxxh0zR
Highlights:
-Fun. Just that: this spec is fun. It's not a good idea, not good for farming heroics, certain death in a raid, and will probably have people asking you what you were thinking. Note that it's basically married to Seal of Blood. Sorry, Alliance brethren. Pull a point out of PoJ for SoC.
-Simply awful survivability. Many of the mitigation and stam talents get skipped. This spec is a statement of confidence in your gear and/or healers. This may seem like a bad idea right out the gate, but it's a BLAST when you're going to be running a lot of instances that you're horribly overgeared for (i.e. helping guild gear up, etc). You will NOT be mana-starved with this spec and will likely top out the damage meters.
-Excuse to break out all that banked Warrior gear with Strength on it and that slow 1-hander with no +dam. If for some strange reason you've wound up with a soulbound Blinkstrike, now's the time to use it.
-The most ridiculous proc strings you'll see this side of Windfury. If you can, get a shaman to come along and prepare to cackle like a lunatic when you see 8 hits off a single swing.... often. Note that this includes 4 SOB self-damage procs. You ARE confident in your healer, yes?
My sig file paraphrase: "Pshaw, real men tank 5-man instances with a 2h'er and sanctity aura.":
http://www.wowhead.com/?talent=sZxbthx0bg0VxVbxxh0z
Variation on the above spec, dropping all the shield-based talents and picking up a bit more stam/mitigation.
Highlights:
-If you're doing anything but trivial 5-mans with this spec your healer must be amazing. Having an amazing healer is great.
-How often do you get to turn a bluetext joke into a spec?