Hurm...'finishing' move may be a bad term to use. Maybe a 'telling' blow may be better. Basically, any move that either:
a) knocks the guy out (I could also say kill, but I won't

)
b) severely injures the opponent so that he/she can't continue fighting. Think busted knee or elbow.
c) stuns the opponent long enough to do either (a) or (b)
What would accomplish the above three really depends on the situation of a particular fight at a particular time. However, 'standard' techniques could be elbows, strong punch to the chin/jawline, strikes to the back of the head/neck, kicks to the knee, kicks to the groin, solar plexus shots to untrained people, etc.
Yeah, 'finishing' technique was a bad term for me to use. I can't say I'd use an elbow as a 'finishing' technique all the time because there would be times when an appropriate target for the elbow would not present itself.
For sparring, submission holds are okay, but I don't know about for the street. Holds that will knock the opponent out (chokes/strangles) are fine, but pain-based submissions I'm not so sure of. Okay, you get the guy to stop fighting or surrender. What then? Eventually, you've got to let him go. Back to square one. However, if you use that hold to go ahead and injure a knee or elbow, that could end the fight. Brutal, maybe, but it's a fight, not a sparring match, yes?
Hurm. I have to stop writing 'stream of conciousness'. Sometimes I don't know if I'm making sense or sounding like some violent crackpot.
Cthulhu