Paladin

Paladins rely on idyllic magic, a variant of divine magic that is more dependent on the caster's ambitions than faith. The first paladin was a disenfranchised policeman, whose city was rife with corruption. He made a deal with the goddess Sentir: in exchange for a unique set of spells, which he combined with his own training, he would root out the corrupt influences in his city and allow true justice to return.
Since then, various "sacred oaths" have been created, one of which must be sworn by the paladin before he receives powers from his divine patron. Unlike clerics, who must remain devout and behave in accordance with their god's tenets, paladins need only offer daily prayers and adhere to their quite secular oaths; while rare, it is possible for a paladin to feel no reverence for his god, though his soul is still claimed by his deity on his death as per their agreement. If a paladin fails to live up to his oath, he will fall from grace and must atone. Unlike clerics, who draw their power directly from their gods, paladins draw it from the oaths they swear, and so cannot become apostates under most circumstances.
Paladins typically gain the ability to Smite their enemies, granting them improved accuracy and damage against those whose alignment falls within their Smite's purview. They can cast a limited number of spells per day before needing to perform a long rest.

Sacred Oath (Associated Divine Domain)

Holy Oath (Justice): Oath to see crimes punished and evil vanquished, and the first sacred oath formed. They gain the ability to Smite Evil but must remain Lawful Good, Neutral Good, or Lawful Neutral.

Gold Oath (Protection): Oath to protect the innocent from harm, even at the cost of letting evil escape. They gain the ability to Smite Evil but must remain Lawful Good, Neutral Good, Chaotic Good, Lawful Neutral, True Neutral, or Lawful Evil.

Silver Oath (Order): Oath of law, created from the belief that a strong system of just laws prevents injustice. Silver paladins are devoted to upholding the law, regardless of the law-breaker. They gain the ability to Smite Chaos but must remain Lawful Neutral, Lawful Good, or Lawful Evil.

White Oath (Good): Oath devised from the belief that all injustice, and from there all suffering, is due to evil in the world. White paladins are fanatically devoted to destroying evil wherever it appears. They gain the ability to Smite Evil but must remain Neutral Good, Lawful Good, or Chaotic Good.

Dark Oath (Retribution): Vengeful version of the Holy Oath, dark paladins are more concerned with punishing the guilty than upholding justice. They gain the ability to Smite Evil but must remain Chaotic Neutral, Chaotic Good, Neutral Good, True Neutral, Lawful Neutral, Chaotic Evil, or Neutral Evil.

Iron Oath (Tyranny): Twisted version of the Silver Oath, iron paladins believe that order must be absolute, and are unconcerned with justice or morality. They will allow lawmakers to violate people's rights so long as the law doesn't forbid it, and they take a letter-of-the-law approach at all times. They gain the ability to either Smite Chaos or Smite Good but must remain Lawful Evil, Lawful Neutral, or Neutral Evil.

Bronze Oath (Liberty): Oath made in opposition to the Iron Oath, bronze paladins believe that personal liberties are the most important things to uphold. While not opposed to law and order, they would rather live in anarchy than under tyranny. They gain the ability to either Smite Evil or Smite Law but must remain Chaotic Good, Neutral Good, Lawful Good, True Neutral, Lawful Neutral, Chaotic Neutral, Chaotic Evil, or Neutral Evil.

Platinum Oath (Nobility): Oath sworn by kings, nobles, elected officials, and others who are to take on the burden of rule. Platinum paladins believe that not everyone is suited to lead but those who do must be held to a higher standard. They gain the ability to either Smite Chaos or Smite Evil but must remain Lawful Neutral, Lawful Good, Lawful Evil, or True Neutral.

Brass Oath (Chaos): Maddened version of the Bronze Oath, brass paladins are devoted to chaos and anarchy. Their beliefs are so disjointed and undefined, attempting to write them down would be futile, though all agree that order is their enemy. They gain the ability to Smite Law but must remain Chaotic Neutral, Chaotic Good, or Chaotic Evil.

Unholy Oath (Hatred): Fallen, twisted version of the Dark Oath, unholy paladins wish to see their enemies suffer, along with anyone associated with them. Whether it be swearing to kill an entire family for their ancestor's slights or justifying genocide, those who swear the oath of hate will go to any lengths for their version of "justice." They gain the ability to either Smite Chaos, Smite Law, or Smite Good, but must remain Neutral Evil, Lawful Evil, Chaotic Evil, Lawful Neutral, True Neutral, or Chaotic Neutral.

Crimson Oath (War): Oath of those whose lives are devoted to battle and conflict. Crimson paladins exist solely to wage war and care little for the reason for it. They may select any single type of Smite but must remain Lawful Evil, Lawful Neutral, Lawful Good, Neutral Evil, True Neutral, or Chaotic Evil.

Dread Oath (Destruction): Some people just want to watch the world burn. Dread paladins are devoted to destruction, whether physical, financial, or emotional. They gain the ability to either Smite Good or Smite Law but must remain Chaotic Evil, Chaotic Neutral, or Neutral Evil.

Hospitaler Oath (Healing): Oath of healing and succor. Hospitalers use their idyllic powers to heal the sick and the injured, only fighting to minimize harm. They gain the ability to Smite Evil but must remain Neutral Good, Lawful Good, Chaotic Good, or True Neutral.

Black Oath (Evil): Oath of evil. Unlike other evil paladins, black paladins know they're the bad guys, and that's the point. Black paladins are evil for evil's sake, driven to a mental place where they believe, rationally, that evil is what the world deserves, or what they want to do. While white paladins must not brook evil under any circumstances, black paladins can pretend to be on the good side, even helping more heroic people out, but only if it is to further the cause of evil in the long run. They gain the ability to Smite Good but must remain Neutral Evil, Lawful Evil, or Chaotic Evil.

Emerald Oath (Time): Oath sworn by those earthlings deputized by the Keepers of Time to hunt down chronomancers at all costs. They gain the ability to either Smite Chaos or Smite Evil but must remain True Neutral, Lawful Neutral, Chaotic Neutral, Neutral Good, or Neutral Evil.

Rose Oath (Love): Oath sworn to promote and protect true love in all its forms. It is quite common for rose paladins to work in duos, such as a husband and wife or a pair of siblings, so long as their love for each other is true. They gain the ability to either Smite Evil or Smite Law but must remain Chaotic Good, Chaotic Neutral, or Neutral Good.

Palladium Oath (Knowledge): Oath to seek and spread knowledge, without limits. They believe that knowledge shouldn't be hidden away or forbidden, often leading them into conflict with more secretive or paranoid organizations, such as the Keepers of Time or the League of Arcanists. They may select any single type of Smite and have no alignment restrictions.

Scarlet Oath (Hedonism): Oath to experience all that life has to offer, whether others like it or not. Scarlet paladins truly are hedonistic and will go to extremes to indulge their whims, even if those they wish to experience something with refuse to consent (or sometimes because they refuse). Believed to be a perverted version of the rose oath, as many fallen rose paladins can be found among the sadistic ranks of the scarlet paladins, though there is little loyalty between them. They gain the ability to either Smite Good or Smite Law but must remain Chaotic Evil, Chaotic Neutral, or Neutral Evil.

Classes

Divine Knights, the default paladins
Crusaders, who give up some magic ability to gain sentinel power armor and barbarians rage
Deathbringers, wicked paladins with greater power, but must remain of an Evil alignment
Detectives, stealthy paladins that are more like rogues than warriors
Dragon Knights (Zalamandi only), more powerful than divine knights but must swear their oath to a dragon god
Esoteric Blades, psychic paladins who add mentalist spells to their repertoire
Magisters, paladin wizards with arcane magic but less martial prowess
Magi, paladins who've fully devoted themselves to their magical powers and do not practice with weapons and armor
Sacred Champions, virtuous paladins with superior magic but who must always remain Lawful Good
Vicars, devout paladins who also get divine magic from their god

Recommended Prestige Classes

Paladin Lords
Chosen Ones
Cyborgs
Dragon Disciples
Living Legends