Just last night I was reviewing some thing for HARP, and I noticed that the Arcane Missile spell is really a pretty nonlethal attack option. It doesn't cause any major wounds, it doesn't cause any bleeds, all it does is some concussion damage and maybe some stun. Even a massively open ended critical only ends up in a practically un-resistable spell.
Since Joe Average has around 40 hits in Harp and fall unconscious at 0 but doesn't start dying until -50, it would take on average 2 4d10 empowered blasts to knock Joe out - but it would take 2 to three more against the unconscious Joe to kill him.
Of course other attack spells may be more efficient against most targets for this (Sleep, etc.).
But as far as for melee combat, the most common answers are just using tiny/small crushing attacks (fists, small clubs, blackjacks) to limit the severity of hit results and using the Subdual rules. -20 to pick any crit on the chart less than or equal to the rolled result can cause more knockouts.
I would even consider making a combat style for this if enough people in the setting actively trained/studied how to do non-lethal attacks. I'd probably take a lesson from Mounted Combat and let the style reduce the penalty, until 0 then let 1/2 any additional skill count as a OB bonus. But before I made such a style fully available in a game I would test this out. I'm a bit concerned that 8DP to pick any crit equal or less than your roll may be a bit too cheap and overpowering, plus I would need to check on the math of (X-20)/2 and see if that would allow PCs to overly exploit the skill cost progression or skill caps.
But I am filled with the picture of Prince Philionel El Di Seyruun yelling "Pacifist Crush!" and "Kindness to All Creatures Kick!"
Regards,
