Chris got to it before I had to say it. As for Captain America, the Brubaker run had been a major success. Also, Captain America was cancelled, because of the platform he was created on. It is hard to continue to market a character that is supposed to be this jingoistic super patriot. World War II was over and Cap was one of the largest propaganda tools of the time. But he did make a come back. Also, I don't know how you can say Iron Man never had a cancelled book.
Tales of Suspense #39-99 (March 1963 - March 1968)
Iron Man and the Sub-Mariner (April 1968)
Iron Man Vol. 1, #1-332 (May 1968 - Sept. 1996)
Iron Man Annual #1-15 (1970-1994)
Iron Man Annual '98-2001
Giant-Size Iron Man (1975)
Iron Man: Crash (1988)
Iron Manual (1993)
Iron Man 2020 (Aug. 1994)
Age of Innocence: The Rebirth of Iron Man (Feb. 1996)
Iron Man Vol. 2, #1-13 (Nov. 1996 - Nov. 1997)
Iron Man Vol. 3, #1-89 (Feb. 1998 - Dec. 2004)
Iron Man: The Iron Age #1-2 (Aug.- Sept. 1998)
Iron Man: Bad Blood #1-4 (Sept.- Dec. 2000)
Iron Man Vol. 4, #1 - (Jan. 2005 - Present) (this series was officially titled as
The Invincible Iron Man in the comic's legal indicia; Retitled
Iron Man: Director of S.H.I.E.L.D. from issue 15 onwards on covers only; the comic book would not officially be retitled until issue 29 (June 2008) in the comic's legal indicia).
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Iron Man: Director of S.H.I.E.L.D. Annual #1 (Jan. 2008)
Iron Man has had plenty of relaunches of titles.