Here is my list. 'Tis a long and extensive one:
Dustin Hoffman as Dutch Schultz in Billy Bathgate. Movie has been derided by critics but I always felt Hoffman did a very good job with the character.
Gabril Byrne as Tom Reagan in Miller's Crossing.
The crazy and always entertaining Johnny Boy in Mean Streets.
Al Pacino as "Lefty" Benjamin Ruggiero in Donnie Brasco.
Steve Buscemi as Tony Blundetto in The Sopranos.
Joe Paltoniano as Ralph Cifaretto in The Sopranos.
Joe Patloniano as Jimmy Murtha in EZ Streets.
Vince Curatola as Johnny Sack in The Sopranos.
Abe Vigoda as Salvatore Tessio in The Godfather. Hated it when he was offed in the end. Shouldn't have made that deal with Don Barzini.
Peter Clemenza in The Godfather. Would have loved to have seen him do the sequel. Too bad Richard Castellano was making unrealistic and dumb demands with his girlfriend about how he wants to have control over his own character's dialogue in The Godfather: part II.
Denzel Washington as Frankie Lucas in American Gangster. Denzel did a great job portraying Frankie Lucas as a debonair, charming, charismatic and moral family man when the real life Frankie Lucas was an uneducated, vile, despicable and immoral human being.
Carlito Brigante in Carlito's Way.
Al Pacino's performance as Michael Corleone in The Godfather: part III. So many aphorisms which is so true in today's world. "Never hate your enemy. It clouds your judgment." This was an underrated movie.