Warpriests with the major blessing Battle Lust turn vicious' backslash damage into nonlethal damage.
Goblin alchemists with the firebrand discovery can set their natural attacks on fire for flaming / flaming burst, taking 1d6 fire damage per round. It's a very... goblinesque ability.
Kineticist's burn is probably the ultimate example for recoil damage.
Ferocity makes you take damage for just attacking, when below 0 HP. You can get a minor version with the combat trait Broken, Not Beaten.
The Bloodbath spell makes you and your targets bleed.
The Detonate spell hurts both you and your targets, too.
That's all I can find for now.
The feat All Consuming Swing lets you cleave and vital strike together, but you also take the extra damage.
If you willingly imbibe a poisonous substance for Gift of Consumption Hex to poison another creature, you could take damage or suffer some ill effect if you fail your own Fort save.
The holy vindicator PrC gets bleeding stigmata which gives them a bonus chosen when the bleeding starts. And yes they're taking bleed damage from that.
I know there's a few ways of getting extra rounds of rage when you take damage, those might be relevant to you.
A hunter with the wild flanking betrayal feat shares that with their animal companion; each does damage to the other when they attack while flanking.
Ninjas can get the redirect force trick - this makes them provoke AoOs for combat maneuvers when they normally wouldn't, and they add the damage they take to their CMB. This is how you dirty trick or grapple demigods or the Oliphant of Jandelay.
There are a number of spells than when cast upon yourself cause any hit against you to deal recoil damage.