Pacino, for example, has had some doozies (Scarface, And Justice for All). Heck I just saw Nicholas Cage go on a hilarious rant in National Treasure II, tho I won’t be nominating him for the top award.
Links to videos of scenes optional but appreciated. Here’s another Pacino, from Glengarry Glen Ross.
Oooh, when it comes to Pacino’s scenery-chewing, the Devil’s Advocate finale is a true guilty pleasure.
John Lithgow in The Adventures of Buckaroo Banzai Across the Eighth Dimension. (cite)
Damn, this is so true. It’s what I came in to post, actually. First thing to pop into my mind.
Peter Ustinov in all of Quo Vadis. My favorite part (which doesn’t seem to be on YouTube) is when he gets the news of Petronius’s suicide.
These clips gives you an excellent example.
Does Nicholas Cage in the horrible Wicker Man remake count? or do I just have to pick one special scenery-chewing scene?
also, a real question: Is “scenery-chewing” always bad acting? Is it defined as over the top?
Well if it is over the top and hamming it up, we are looking for, R Lee Ermey in Full Metal Jacket probably has a shot. Obligatory YouTube link (like you don´t have it book marked anyway)
For me, “chewing up the scenery” means “over the top.” Unfortunately, “over the top” often is a result of bad acting, but when it’s not, it’s wonderful!
Warren Beatty in Bugsy, specifically the scene of him in the jail. Can’t find a YouTube link, but it was some histrionic acting. And Annette Bening sitting there calmly waiting for the tirade to subside makes it even better.
DeNiro in Cape Fear. Way over the top! 
Are we counting Jack Nicholson in The Shining?
While Pacino is a true master of scene mastication, my true favorite is Alec Baldwin’s famous monologue in Malice. Do I have a God complex?
Rod Steiger and James Woods leave no scenery unchewed in the otherwise execrable Sylvester Stallone/Sharon Stone vehicle The Specialist, but I’m going to have to give it to Steiger on points for his Cuban accent: “Chew fin’ heemp an’ chew breeng heemp to me.”
Jeremy Irons in Dungeons & Dragons was pretty entertaining to watch. It was pretty much the only positive thing in the movie, though.
I think the poster child example is Brian Blessed as Prince Vultan in Flash Gordon.
Bette Davis in Dark Victory. When Judith finally declares I think I’ll have a large order of prognosis negative! it concludes one of the greatest scenery meals of all time.
Brian Blessed is my all-time favorite. The man lives on an all-scenery diet.
My favourite Brian Blessed scenery-chewing moment is from his role as Augustus in the TV series “I, Clavdivs”…
IS THERE A MAN IN ROME WHO HAS NOT SLEPT WITH MY DAUGHTER?!?!?!?!
Although he also gets a really moving and extremely understated moment with Augustus’ death…
Just my 2 eurocent!
The ultimate prop-mastication film…Mommy Dearest. Faye Dunaway in a FEAST of epic proportions.
“YOU MANIACS!!! YOU BLEW IT UP!!! DAMN YOU!!! DAMN YOU ALL TO HELL!!!”
I love that movie. And he leaves no scenery unchewed. It is all thoroughly chewed, then swallowed, partially digested, regurgitated, and then chewed again, like a cow chewing his cud.