First one that popped into my mind was Mir vs Kongo. Twas a thing of beauty.
After reading the one dude's Faber reference, i immediately thought of his finish on Bowles. Right up there for one of the best subs of all time.
Obviously knocking a guy out cold is pretty decisive when it comes to finishing a fight. It's no more decisive than choking a guy to sleep though. Rendering a guy unconscious is pretty goddamn decisive. It's all the same, the only i difference is how you get there.
That said, it's hard to argue that beating the shit out a guy for 25 straight minutes isn't extremely decisive as well. Gsp won multiple fights in which his opponents never had control for more than 10 seconds at a time.
What i'm basically saying is, there are plenty of ways to win a fight decisively. Is the knockdown + sub the best example? Perhaps. It's probably the funnest to watch.