From Wikipedia. Here are a few
Typically, write-in candidates have a very small chance of winning, but there have been some strong showings by write-in candidates over the years.
Presidential primaries
In 1928, Herbert Hoover won the Republican Massachusetts presidential primary on write-ins, polling 100,279.
In 1940, Franklin D. Roosevelt won the Democratic New Jersey presidential primary with 34,278 write-ins.
In 1944, Thomas Dewey won the Republican Pennsylvania presidential primary with 146,706 write-ins. He also won the Oregon Republican presidential primary with 50,001 write-ins.
In 1948, Harold Stassen won the Republican Pennsylvania presidential primary with 81,242 write-ins.
In 1952, Robert Taft won the Republican Nebraska presidential primary with 79,357 write-ins.
Also in 1952, Estes Kefauver won the Democratic Pennsylvania presidential primary with 93,160 write-ins.
Also in 1952, Dwight Eisenhower won the Republican Massachusetts presidential primary with 254,898 write-ins.
In 1956, Dwight Eisenhower won the Republican Massachusetts presidential primary with 51,951 write-ins.
In 1960, Richard Nixon won the Republican Massachusetts presidential primary with 53,164 write-ins.
Also in 1960, John F. Kennedy won the Democratic Pennsylvania presidential primary with 183,073 write-ins, and he won the Democratic Massachusetts presidential primary with 91,607 write-ins.