Here's some thoughts on likely LK builds for Holy paladins. Again, it's still in beta, so things may change drastically.
48/0/23 - Sheathbot
This looks to be the best single-target healing build you can make. It has the most spell power, the most crit, and a massive 2.4x crit multiplier. (For reference, a normal paladin has a 1.5x multiplier.)You also provide Imp Might and 3% crit for the raid.
I think this will be the standard 25-man raiding build, at least for the first Holy paladin in the raid. You are giving up any chance of an AoE heal, but the druids, priests and shamans can cover that while you concentrate on keeping the main tank up.
51/0/15+5 - Beacon of Light + Ret
This build trades-off the extra spellpower and crit multiplier from the previous build in exchange for an AoE heal in Beacon of Light. Basically you trade raw single-target healing in exchange for flexibility. You also provide Imp Might and 3% crit for the raid.
I think this build will be very popular for 5 and 10-man instances. Since you have fewer other healers (or none) to cover your weaknesses, flexibility becomes more important.
51/20/0 - Beacon of Light + Prot
Trade the goodies in Retribution for Blessing of Kings, Imp Devo Aura, and Divine Guardian. Also get Beacon of Light for some AoE healing.
Essentially, this is the "We don't have a Prot Paladin and people are whining for Kings" build. It should be pretty good for the second Holy paladin in a 25-man raid.
Edit: On EJ, Cathela posted an interesting way of looking at 25-man raid composition for paladins. Positing two default slots per class (fair, considering there are now 10 classes), Cathela proposes that it will break down as follows:
Slot 1: Sheathbot or DPS Ret Paladin
Slot 2: Beacon of Light + Prot or Tank Prot Paladin