Harry Truman. Free frank
"Harry Truman" as ex-President on color picture post card depicting
the Truman Library, to Springfield Ill., "New York N.Y. Dec. 31, 1959"
cancel, Very Fine, the Act of 1957 gave him franking privileges (Image) 
Dwight D. Eisenhower.
Free frank and censor's marking "Dwight Eisenhower" with
"Free" at top right on legal-size Officer Courier service cover to
Mrs. Eisenhower in Washington D.C. and forwarded to Ft. Benning Ga., red
Army Examiner's handstamp, Dec. 10, 1944 receiving datestamp, with original
autograph letter signed "Ike" to "Darling", Very
Fine, Eisenhower's signature on this letter to his wife served double duty,
as both a censor's marking and free frank, this letter was written six
months after the Normandy invasion and states "He will tell you of my
impending trip home -- there are so many complications involved that it
would take me hours to try to write about them." (not to mention
military secrecy) (Image) 
Dwight D. Eisenhower.
Free frank as President "Dwight D. Eisenhower" as President
on cover to El Paso Tex., Washington D.C. Jun. 19, 1960 machine cancel,
Very Fine, Eisenhower's autograph free frank as President is rare --
earlier military franks are more common and presidential franks are usually
facsimile signatures (Image) 
John F. Kennedy. Free
frank "John Kennedy" as Senator on cover with "Palm Beach Fla. Jan.
19, 1955" machine cancel, U.S. Senate corner card in blue, pristine
conditionEXTREMELY FINE. ONLY TWO EXAMPLES OF KENNEDY'S AUTOGRAPH FREE FRANK ARE RECORDED. A MAJOR 20TH CENTURY RARITY.
Although facsimile signatures are common from this period, only two examples of a free frank in Kennedy's own hand are recorded.
Ex Kantor (Image)
John F. Kennedy. Hurried
autograph on oversize card with cachet of PT 109, 4c stamp tied by "U.S.S.
Joseph P. Kennedy Jr. Aug. 1, 1961 A.M." postmark, purple "U.S.S. J.P.
Kennedy, New York N.Y. Aug. 2, 1961" double-circle datestamp, fresh and
Very Fine, scarce genuine signature, accompanied by autopen (for
comparison) on Jan. 21, 1961 cover from second day in office (Image) 
Lyndon B. Johnson. Bold
free frank "Lyndon B. Johnson" as ex-President on cover with Austin
Tex. Dec. 4, 1970 machine cancel, originally sent by collector Fred Casoni
who had obtained Johnson's signature and addressed the envelope in pencil
to himself, at a later date the address was mostly erased by Casoni
(although it is partly visible), Very Fine, ex Joyce, Hart and Kantor,
accompanied by a short history of this cover written to Morton Dean Joyce
(Image)