First, let's make the assumption that there is a warrior or druid MT, and the paladin is the OT. Would a build like 0/19/42 be better than the standard full protection build?
Retribution OT Build: 0/19/42
(Switch points from Anticipation to Precision once you have the necessary defence from gear.)
The big difference is that the Ret paladin is not going to be crush immune, but the Warrior/Druid MT is the one going to be handling the bosses and worrying about crushes. Combined with decent tanking gear, this build is more than sufficient to handle all non-73 mobs.
And once tanking duties are finished or not necessary, this build can pull out a 2H and add significantly more damage. If the paladin is in a DPS group, they can even switch to Sanctity Aura and boost everyone's damage.
(Just to be clear, if you are tanking anything during the fight, you are wearing tank gear, not Retribution gear.)
I don't think that this build will be sufficient to MT anything, but given that most groups already have a warrior (or druid) MT available, this build might be a more useful OT build than a Protection build.
You could also do a similar build but go Holy. However I don't think it would work as well, due to limited mana and +healing in tank gear. As well, if a normal 10-man has 2 tanks/3 healers/5 dps, one tank fights would be better off as 1 tank/3 healers/6 dps, rather than 1 tank/4 healers/5 dps.
The increased damage Retribution brings synergizes well with generating threat as an OT. This build would also bring 3% crit for the raid, allowing you to get the increased threat from Judgement of the Crusader at the same time, and Sanctity Aura for the DPS group.
I'm seriously considering respeccing to this build. I'm generally last on the tanking depth charts for my guild, so I never actually need to main-tank. This would make it a lot easier to maintain threat right behind the main tank, as well as be more useful in a fight like Shade of Aran.
The biggest thing stopping me from respeccing is 5-man play. Would this build be enough to tank a 5-man, or what other role would I take up? I am leery of a Ret paladin's viability in an actual DPS slot, at least with the gear I have. (Let's put it this way: I think I have less than 1000 AP in my DPS gear.)