I just was about to quote that same post for that same reason. (I also recently say Key Largo for the first time and he’s good in that, but he’s GREAT in Double Indemnity.)
How could I forget Key Largo? “Yeah, that’s it. I want MORE.”
I’ll buy that, but it applies just as much to Cruise as it does to Hoffman.
By the same token, I’m not saying Hoffman’s performance in the leading role didn’t deserve the awards it got; I’m merely saying Cruise’s performance in the supporting role was, y’know, underappreciated. (Compare it to, say, The Color Of Money, where Cruise wasn’t required to do nearly as much in the supporting role, and, sure enough, didn’t; Paul Newman got a leading-man Oscar for that one by playing an interesting guy who reacts to people around him in entirely human ways: he’s charming, he’s dismissive, he’s irritated, he’s humbled, he patiently explains stuff, he’s got something to prove, you get the idea. He doesn’t need someone else to do most of the work; he just needs someone who doesn’t screw up.)
The Stranger is Edward G’s best. Sorry, Cincinnati Kid fans (I know, I like that movie too, and Eddie G is, as always, the top man, but even as a non-card-player, the notion that the guy with the relatively unlimited money will always win no matter what, just by constantly reupping and buying every hand is too much for me).
I forgot about Key Largo too. Should watch that again soon. I can’t watch Double Indemnity anymore – Barbara Stanwyck makes my arm sore.
And he did it all by recycling Casanova Frankenstein and ever other hammy eccentric Rush always plays. He can be amusing to watch, sure, he may even garner the odd award for it, but as an actor Rush is a one-trick pony.
Monty Python and the Holy Grail.
Graham Chapman plays Arthur - the sane character whom all the idiots revolve around.
Manages to be the funniest character in the film.
Alan Bates in The Boys in the Band. Emory, the guy who’s hilariously obnoxious at first, then goes off on the (allegedly) straight guy, then gets the longest and most poignant segment in the phone game sequence, telling about his high school crush. I think if that film were released today, as a period piece, he would get a Best Supporting nomination.
I love when Harrison Ford says to that guy, “GET OFF MY PLANE!!!” in the Air Force One film. 
God bless you and them always!!! 
Holly
P.S. So far that is the only film with Gary Oldman that I have seen.
Colin Farrell in In Bruges.
Daniel Craig in Flashbacks of a Fool.
John Cusack in The Ice Harvest.
John Goodman in The Big Lebowski.
Steve Buscemi in Ghost World.
Alanna Ubach as Naomi, the passive aggressive waitress in Waiting.
Nick Stahl as That Yellow Bastard in Sin City (and drool-worthy pre-yellowed.)
Joseph Gordon-Levitt as Jimmy in H20: Halloween Twenty Years Later (very good sequel to the original Halloween), and as George in Roseanne.
Chris Kattan from House On Haunted Hill.
Samuel Jackson Jr. in Pulp Fiction
Jack Nicholson in The Witches of Eastwick
Peter O’toole in Lawrence of Arabia
Humprey Bogart in The Caine Mutiny
Robert Shaw in A Man for all Seasons
John Voight in Midnight Cowboy
The winner of this thread is of course Val Kilmer in Tombstone.
On a more current note, Harrison Ford in Cowboys and Aliens. Maybe not good enough to win but at least good enough for a Supporting Actor nom.
Val Kiklmer in Tombstone is an excellent suggestion. Assuming it never got a nomination, which I find hard to believe.
I was going to say, Stanly Tucci in any movie he’s ever made. But just to follow the rules, I’ll nominate his performance in Big Night.
I was assuming the Mtv Movie Awards didn’t count (and he didn’t win).
How on earth does that count as “under-appreciated”? O’Toole was nominated for “Best Actor”, and his Lawrence is widely recognized as one of the great movie performances of all time.
The OP’s criterion was
I don’t know how your other suggestions stack up against that criterion, but O’Toole’s Lawrence fails hard.
Fail: nominated for Best Supporting Actor.
Possible fail: won NY Film Critics’ Circle and LA Film Critics’ Association Best Actor?
Fail: nominated for Best Actor.
Fail: nominated for Best Supporting Actor.
Fail: nominated for Best Actor.
I nominate the_diego for Poster Most Unclear on the Thread Topic. 
Terry Kiser in Weekend at Bernie’s