Ever since Ultimate Intrigue came out I've been, er, intrigued by the potential of memory modification magic to help in intrigue/nonviolence campaigns. The First World included two really strong abilities in that vein, so I thought I'd start an effort to crowd source all of them and discuss the best options. Please add anything I don't include below.
Spells:
Memory Lapse: A weak introductory option, wipes out memory of the previous round.
Modify Memory: The standard, this one isn't actually very good because the permanent nature makes it subject to detection and it can be dispelled.
Out of Sight: This is pretty great, every observe has to save or forget that he saw you and what he saw you do. Min/level duration.
Amnesia (Villain Codex): Allows a total mindwipe, taking away all memories and class abilities. Useful for reprogramming someone as part of a long-term plot, maybe.
Fleeting Memory: Wipes out future memories (round/level) after you cast it. Useful for a quick interrogation, theft or, other quick and dirty misbehavior that you don't want remembered.
Dream Reality (Inner Sea Intrigue): This is like Fleeting Memory, but lasts min/level and is Illusion for those who specialize in that. The ultimate for a one on one interaction with someone you don't want to remember the details of later, but at level 6 it's pretty expensive.
SLAs:
Occultist Psychic Curse: Allows you to make a target lose its memory for one HOUR per level. Top shelf for making unwitting allies you mind controlled go at no small risk to yourself. Such big gaps with nothing to fill them may not always be the best option, though.
The Lost Prince's obedience (First World campaign setting) second boon gives you three per day Modify Memory, but only requires a standard action. Use two uses to modify one hour for one target. Use all three uses to modify one day for one target. This lets you fill with new memories, not simply leave a blank. The best option, but requires a dedicated build.
Monsters:
A few outsiders have Modify Memory as a SLA. It's not a the best spell when you cast it, it's not better when a called outsider does it for you. Let's look at more interesting things with unique abilities or better action economy in using effects similar to Modify Memory. Maybe you can summon, recruit, or enchant one of these to help you.
Gerbie (First World campaign setting) has a touch attack that wipes away memories as per Modify Memory, but does it instantly and NO SAVE. Evil parties will want to have a charmed Gerbie along as a memory wiping machine, good parties might want to recruit one as a helper or cohort.
Rakshasha, Raktavarna: An (evil) improved familiar option, this guy's poison makes the victim forget a minute of interactions with it. Not a great option given the bad DC and that it only wipes memory of your familiar, but it exists.
Hyakume: It's weird, it's CR 15, but if you can get one on your side its Memory Drain ability might be useful to you. Maybe.
Gray: They're humanoid, dominate away! Very limited in their abilities, but if you regularly want to get information from sleeping targets, having one of these by your side is a help.
Psychopomp, Viduus: A melee attack does Modify Memory on a target, or completely wipes the memory of an undead. I don't know why you'd want to leave an undead with no memory "alive" behind you, but this is probably the only way to do that if you do.
Vampire, Vetala: Grappling isn't the most efficient way to apply Modify Memory, but it's better than 5 minutes and no save.
Devil, Mnemor: I didn't mention Repress Memory above because while it's a great memory modification spell, it only works on the caster. Guess what? This guy can apply it to someone it hits in combat.
So that's a lengthy list of spells, abilities, and monsters you can try to use to modify memories if you need to leave someone alive. What am I forgetting?
Anonymous interaction - targets forget most information about you.
Forgetful slumber - one target 10 HD or less falls asleep & forgets last 5 min.
Hidden diplomacy - makes target forget you intimidated them, even if the intimidate made them do something.
Aura of the unremarkable - not exactly memory modification, but people accepting everything you do as normal is in the same vein.
Edit: & psychics with the dream discipline get to mess with peoples' minds and memories too. I suspect there's other dream-themed abilities which could do likewise.