“The difference between myself and Castro is that I am not aligned and he is; I am a socialist and he is a communist.”

As quoted in Hitler and I, Otto Strasser, Boston, MA, Houghton Mifflin Company (1940) p. 106
Other remarks

The presence of a person who has strong political convictions always sends me flying off in a contrary direction. Inevitably, in the world of today, this will bring me before a firing squad sooner or later. Maybe the fascists will shoot me, and maybe the proletariat, but political contrariness will be the end of me; I feel it in my bones.
The Diary of Samuel Marchbanks (1947)

Responding to a question at his press conference (February 28, 1947); reported in Public Papers of the Presidents of the United States: Harry S. Truman, 1947, p. 191

As quoted in the Evening Herald in Dublin, Ireland (February 3, 1948), reprinted in Economic Council Letter, Issue 278, Part 397 (1952), p. 1807 https://books.google.com/books?id=qtAeAQAAMAAJ&focus=searchwithinvolume&q=first+rate+Fabian
1940s and later

Daily Express, 5 July 1945.
Winston Churchill supporting Morrison's opponent in the 1945 general election.
About

Reported by Paul Scott in the Lewiston Daily Sun (27 September 1972) again as remarks at Duke University; http://news.google.com/newspapers?id=FXwgAAAAIBAJ&sjid=7mcFAAAAIBAJ&pg=1010,3814989 reported elsewhere as a remark made at Michigan State University (22 November 1970) and cited to the Detroit Free Press but without a date, page or headline.
Rick Perlstein, in a 2005 London Review of Books article and in his 2008 book Nixonland: The Rise of a President and the Fracturing of America (Simon and Schuster, p517 http://books.google.com/books?id=dM_enWzoghoC&pg=PA517#v=onepage&q&f=false), accused Helms of inventing the quote: "They tapped their network of friendly media propagandists, like the future Senator Jesse Helms, then a TV editorialist, who supplied an invented quotation that still circulates as part of the Fonda cult’s liturgy." http://www.lrb.co.uk/v27/n22/rick-perlstein/operation-barbarella The COINTELPRO Papers (2002) documents a separate attempt to plant false quotes from Fonda in the press.
Disputed

The accusation of inconsistency has no foundation. My conduct has always been straight in the sense of looking at the substance of things and not to the form. I adapted socialisticamente to reality. As the evolution of society belied many of the prophecies of Marx, the true socialism folded from possible to probable. The only feasible socialism socialisticamente is corporatism, confluence, balance and justice interests compared to the collective interest.
As quoted in “Soliloquy for ‘freedom’ Trimellone island”, on the Italian Island of Trimelone, journalist Ivanoe Fossani, one of the last interviews of Mussolini, March 20, 1945, from Opera omnia, vol. 32. Interview is also known as "Testament of Benito Mussolini, or Testamento di Benito Mussolini. Also published under “Mussolini confessed to the stars”, Publishing House Latinitas, Rome, 1952. (Intervista di Ivanoe Fossani, Soliloquio in “libertà” all'isola Trimellone, Isola del Trimellone, 20 marzo 1945)
1940s

"Only Weak Communism Can Save Us" (2013)

Peter Longerich, Goebbels: A Biography, New York, NY, Random House (2015) p. 26, “Erinnerungsblätter,” 27, (diary entry: 1924)
1920s