I have three at the top of the list right now. I like Chuck's TKO on Tito, Rich Franklin's knockout on Nate Quarry, and Melvin Guillard's knockout on Rick Davis.
As far as people I'd like to see get knocked out. It would have to be someone really cocky like Brandon Vera. After he won his first fight he called out Chuck Liddell and said after he won heavyweight belt he was going to drop down and take on Chuck.