With a reservation about 1992, I agree with John’s correspondent’s list. In 1844 the Liberty Party (die-hard anti-slavery) kept Henry Clay out of the White House by siphoning enough votes from him in New York to tip the state and the election to James K. Polk. In 1848 the Free Soil Party (also anti-slavery) eviscerated Lewis Cass in New York, tipping state and election to Zachary Taylor. In 1844 the Liberty Party was arguably counterproductive, since Polk was affirmatively pro-slavery while Clay was a hedger. But in 1848 the Free Soil Party arguably served its own goals since Taylor turned out to be more anti-slavery than Cass would have been.
I say arguably because third parties often operate on the psychology of the worse, the better.
The one and only.