Sean Penn won the best actor Oscar this year for his searing portrayal of grieving father Jimmy Markum in Mystic River.

Indeed, he was excellent.

But the conventional wisdom in Hollywood is that the award was more of an honorary Oscar for Penn's extraordinary career up to this point than it was recognition for his work in that single film.

I tend to agree that he's had many finer moments, and if the Mystic River win puzzled you at all, you ought to check out these ones. Then you'll understand.

'Casualties of War' (1989)

The commanding officer of a five-man Vietnam patrol unit, Penn's Sgt. Meserve spearheads the abduction, rape and murder of a Vietnamese peasant girl with the carefree swagger of a joyriding teenager. But Penn manages to infuse this monstrous individual with enough submerged humanity that he always comes across as a frighteningly real person.

His best scene: After raping their victim, Meserve confronts Michael J. Fox, the lone virtuous soldier, who stands outside the hut watching the atrocities unfold in the middle of a rainstorm. Between ominous flashes of lightning, Meserve shouts his own version of Psalm 23, complete with a memorably belligerent twist.

'Hurlyburly' (1998)

Hurlyburly is a strange little movie about a group of sleazy, cocaine-addicted Hollywood figures and their tragicomic obsession with semantics. Penn plays Eddie, the only one of the bunch who still has some remnants of a soul.

His best scene: Eddie explodes with rage at his girlfriend because she can't decide whether she wants to go to a Chinese or French restaurant. This is a delicate, difficult scene to play seriously, but Penn delivers it in a way that makes it seem totally instinctual and genuine.

'The Thin Red Line' (1998)

As cynical WWII Sgt. Welsh, Penn shares a few brief philosophical exchanges with Private Witt (the recently crucified Jim Caviezel), which demonstrate the quiet poetry that lurks just beneath the film's machine-gun-heavy surface.

His best scene: Kneeling over Witt's grave, Welsh manages only one line, but it's obvious Penn could have pulled the intensely emotional scene off with no words at all. It isn't the fact that Welsh is holding back tears that endears him to us, but the damaged, dignified manner in which he holds them back.

'Sweet and Lowdown' (1999)

Penn plays fictional '30s jazz musician Emmet Ray, the second greatest jazz guitarist in the world. He's a selfish, vulgar, gluttonous narcissist, and yet one of the most loveable protagonists I've ever seen in a film.

His best scene: The last time Emmet sees sometimes lover Hattie is unforgettable. I won't spoil this moment for those who haven't seen the film, but I'll describe it. What he is saying and what he is actually feeling are two extremely different things. Only a superb actor can make the latter more resonant than the former, and Penn does exactly that here, more effectively than anyone else in recent memory.