I'll add:
"Al Capone," basically a B-movie but with an electrifying performance by Rod Steiger in the title role. He was hands-down the best of all the movie Capones and Capone-like characters.
"The Brotherhood," a much-underrated Mob movie with Kirk Douglas very good as an old-fashioned Sicilian-American Don struggling--fatally--with the modern Mob and his own wannabe younger brother
"Honor thy Father," a TV movie based on the Gay Talese book about Bill Bonanno and faher Joe, with four memorable performances by Joseph Bologna, Brenda Vaccaro, Raf Vallone and Richard Castellano. The script mercifully omits all the "man of honor" BS that Bill Bonanno loaded on Talese in the book.

Though it is not a Mob movie per se, "White Heat" is the greatest gangster movie ever made. James Cagney at his most forceful as Cody Jared, psychopatic killer and leader of a gang of payroll robbers.