For campaign I'd like to run, I remove the alignment restriction (as there is none in this campaign except for outsiders, and most of the paladins would be LN or LE if there were) and swap out abilities based on which order of paladins the person is in. The abilities that get swapped out are Detect Evil, Smite Evil, Turn Undead, and Remove Diseas; each remains, but affects something different. Champions of Valor does a little of this, and it is what inspired me. Turning has been generalized to channeling in my campaign.
Order of Marka
The Order of Marka is devoted to Arlat; its purpose is to destroy users of foul magic, such as druids, warlocks, and spell-singers (though this task is often handled by senior paladins, or handed off to members of the order of Jareth).
Detection: Magic.
Smite: Magic-using creature (Bard, Druid, Hexblade, Warlock, creatures with (sp) abilities)
Channeling: Divine Interdiction.
Weekly Power: Spellshatter (See Champions of Valor, page 46).
The only legal magic in this setting is that practiced by the clerics of the Four.
Divine Interdiction [Channeling]
You can channel positive or negative energy to disrupt and enemy spellcaster.
Prerequisite: Ability to channel.
ib]Benefit[/i]: Choose an enemy within close range (25 ft + 5 ft / 2 channeling levels). Expend a channeling attempt and make a channeling check with a +4 bonus. If the result of the channeling check is positive, apply a penalty to the targeted creature’s caster level for spells and spell-like abilities equal to the result of your check. This penalty lasts for 1 minute, unless the victim makes a will save, at which point it lasts 1 round.
The result of the channeling is the same as the modifier from the "Most Powerful Undead Affected" column of the Turn Undead table in the PH (though I have extended the table). This will turn off a caster's highest-level spells/invocations and weaken the ones they keep. It might be too powerful, I haven't tested it.
Two more of the Palladin orders:
Order of Elter
The Order of Elter is devoted to Marlish; its purpose is to destroy undead and those who deal with them. This is the second-largest order of paladins.
Detection: Undead.
Smite: Undead.
Channeling: Turn Undead
Weekly Power: Halt Undead.
Order of Gelt
The Order of Gelt is devoted to Zirth; its purpose is to protect and heal others.
Detection: Life.
Smite: You may smite those who threaten an ally, or have harmed an ally in the last 5 rounds.
Channeling: Sacred Healing.
Weekly Power: Remove Disease.