BJ Penn vs Sean Sherk. Sherk only attempted 2 takedowns in that 15 minute fight so it was a nonstop standup fight. BJ threw maybe 2 kicks everything BJ did was off his jab that night and it setup the uppercut that rocked Sherk and of course BJ eventually stopped him.
The boxing display that BJ showed against Diego was the best ever IMHO in the history of MMA. His jab, timely aggression, counterpuching was sharp and he got hit once by an elbow nonetheless. Silva/Forrest is up there to as far as the showboating aspect of boxing
Paul Daley has showed some good boxing skills in his fight though silva and griffin fight stands out for counter punching.
The old saying is the last thing for a puncher to lose is his power. And for a old bugger Mercer hit Sylvia with a shot for the ages.
Couture's victory over Liddell was a great example of using boxing to win a fight. Couture established his jab from the outset and was able to throw Liddell's timing off for the entire fight. Obviously Couture used wrestling in conjunction with his boxing to secure the victory - this is mixed martial arts after all - but it all started with his establishing the jab.