Cleveland Browns, 1946-(year)
The original Browns were the dominant team of the old All-American Football Conference, a rival league which operated from 1946 to 1949. Named for their coach, the innovative [Paul Brown]?, the team was admitted into the NFL following the AAFC's demise, and went on to play in the NFL championship game each of the next seven seasons, winning three times.
After Brown was dismissed following a disappointing 1963 season, coach Blanton Collier led the team to its last NFL championship in Cleveland in 1964.
Baltimore Ravens, (year) to present
The Ravens are the reigning NFL champions as of this writing, having won Super Bowl XXXV in January, 2001.