So after looking over the advanced class guide, I finally came up with a great archetype for the anti-paladin class....
The Unholy Assassin
While most antipaladin's crave the power and protection provided by their dark patrons, others choose to forgo such gifts in order to slay their enemies regardless of their allegiance.
Class Skills: An unholy assassin gains survival as a class skill.
Skill Ranks Per Level: 4 + Int Modifier
Studied Target (Ex)
At 1st level, an unholy assassin gains the slayer's studied target class feature. He uses her antipaladin level as his effective slayer level to determine the effects of studied target.
This ability replaces smite good.
At 3rd level and every 3 levels thereafter, an unholy assassin selects a slayer talent. Starting at 12th level, he can select an advanced slayer talent in place of a slayer talent. He uses his antipaladin level as his slayer level to determine what talents he can select.
This ability replaces aura of cowardice, cruelty, and plague bringer.
Marked for Death (Ex)
At 11th level, an unholy assassin gains the quarry class feature; this functions like the slayer ability of the same name.
This ability replaces aura of vengeance.
Doomed to Die (Ex)
At 17th level, an unholy assassin gains the improved quarry class feature; this functions like the slayer ability of the same name.
This ability replaces aura of depravity.
Vassal of Darkness (Ex)
At 20th level, an unholy assassin gains DR 10/good and becomes a master of murder. As a standard action, he can make a single attack against a studied target at his full attack bonus, choosing one of the following effects: kill, knock unconscious for 1d4 hours, or paralyze for 2d6 rounds. If the attack succeeds, the target takes damage normally and must succeed at a Fortitude saving throw or suffer the additional effect. The DC for this save is 10 + 1/2 the antipaladin's level + the antipaladin's Charisma modifier. Whether or not the target succeeds, it cannot be targeted by this ability again (by any slayer) for 24 hours.