I like your question. It is extremely broad. Looking for points that cause "scamage or some sort of reaction." I gotta tell you man, almost everything you do will cause a reaction. If you dropped to a knee and punched my leg, it would both cause damage and a reaction, albeit not a terrible amount of either.
I train in Brazilian Jiu Jitsu, Western Boxing, and Thai boxing and what I can tell you is that there are extremely useful VITAL points on the body, but the ones i'll reference aren't what you're looking for in all likelihood.
In muay thai, we use hard round kicks to the thigh constantly and take many in a fight. That being said, without training, the average human couldn't take a single thai kick to the thigh and keep standing. The leg is extremely "vital" to your ability to continue moving and if you ever get the chance to see a thai fight you might just be amazed at how much damage a swift thai kick can do to a leg in a small amount of time. I'd mention the skull, but everyone is aware of strikes to the head and jaw i think at this point.
In jiu jitsu, we manipulate a person into positions that cause pain or loss of function and usually both. Moves like armbars, omoplatas, triangle chokes, Kimuras, all of these moves will at some point cause enough pain for a person to tap. If the person is amazingly pain tolerant, then of course you'd have to break the arm, dislocate the shoulder, or choke them unconsious which is at that point quite easy in most cases once the submission is applied.
In boxing, i won't mention blows to the face as stated above, but another thing that nobody knows about(unless you train) is the liver. Hitting to the kidneys hurts, and it can cause longterm damage. It should be avoided. But the LIVER is a terrible thing to have damaged. Blows to the liver end fights quicker than they began time and time again when a trained professional makes the strike. It is not so tiny and hard to damage as the pressure nerve points in the body, but i promise you, it is at least as if not more powerful in ending an assailent's charge, and much easier to access. To hit the liver you need only throw a left hook to the body right under the ribs. The more you angle the hook up toward the oposite side shoulder the more likely you will do liver damage. This is difficult to do with boxing gloves on, but with MMA gloves it is a cinch, and barenuckle you really have to not get punched in the liver if you know what's good for you. Another common way to attack the liver is with a left thai kick to the body. Fighters like Mirko "Crocop" Filipovic have demonstrated on several occasions the power of a liver kick whether it be on the giving or the recieving end. The best thing about liver blows is that once you cause someone to whince, or drop from one, the liver is in an incredibly unstable state, and any more impact to it will cause extreme pain even if it is a light strike or a blocked punch/ thai kick.
Well, there you have it, some lesser known, nerve unrealated vital points in the body that will end a fight. Just like the other nerve points (of which i have not studied) it takes practice to get a good liver shot or leg kick. You can shrug it off after failing at it a few times but trust me, they work. And if you dont' trust me, watch some K-1 or MMA and you will see what i'm talking about.
I hope you learned a lot from all these great posts and remember that noone is 100% right on this one it is still under hot debate by martial artists all over so take each answer with a grain of salt. The only thing I really recomend is that you never get caught talking about a death touch or death strike, for that will get you laughed at in manymany circles whether or not it exists it is commonly "known" to be fiction.