The Dallas Cowboys helmet. Don't email, I've already heard it about the following statement: I like the 1960-1963 version. So there. In 1964, the white background was replaced with silver.
The Cowboys have essentially had the same design on their helmet since 1967. During the 1976 season, a red stripe honoring the USA's bicentennial was worn during some games.
Latest update: the Dallas Cowboys plan on wearing the white helmet this Thanksgiving Day 2004!