NONE. Maybe this has been covered in the past. But I've heard for so many years from so many fans that I did some research and confirmed that the polls are MORE THAN fair to Nebraska.
I looked at FINAL AP rankings from 1970 to present and found that multiple times the Huskers were the highest rated team with one, two, three and four losses. Like this:
1972 Final rank #4 Record 9-2-1 No two loss team was ranked higher
1973 #7 9-2-1 Again, no two loss team higher
1974 #9, 9-3 No three loss team higher
1976 #9, 9-3-1 Same as above
1981 #11, 9-3 Same as above
1984 #4, 10-2 No two loss team higher
1985 #11, 9-3 No three loss team higher
1986 # 5, 10-2 No two loss team higher
1987 #6, 10-2 Same as above
1996 #6, 10-2 Same as above
1998 #19, 9-4 No four loss team higher
2009 #14, 10-4 Same as above
And don't forget, Nebraska had a golden oportunity way back at the end of the 1981 season to be the forst National champion with TWO LOSSES!