So I did some digging to see just how great some of these dynasties actually were. Here are some of the greatest teams ever. I was looking at a minimum 4 year stretch of fewest losses:
Alabama (2008-present): 65-7
USC (2002-08): 80-9 in 7 seasons. 34-game winning streak from 2003-05
Miami (2000-03): 44-4 in 4 seasons. 34-game winning streak from 2000-02
FSU (1992-99): 88-9 in 8 seasons
Nebraska (1993-97): 60-3 in 5 seasons

26-game winning streak from 1994-96
Notre Dame (1988-93): 64-9 in 6 seasons
Miami (1985-92): 88-8 in 8 seasons. 29-game winning streak from 90-92
Alabama (1977-80): 44-4 in 4 seasons. 28-game winning streak from 78-80
Alabama (1960-66): 68-6 in 7 seasons