Didn't get a ton of traction on Indiana, so here's #3
1936 - obviously nobody here can speak to it, and can't find much info. Went 7-1 overall, 6-0 in the Big Ten, winning the title, and finished #7 in the initial AP Poll, which is tied for their all-time highest finish.
1948 - again, nothing, but went 8-2 overall, 5-1 in the Big Ten, 2nd to Michigan. Because of the no repeat rule back then, UM couldn't go back, so Northwestern went, and beat Cal 20-14 for the lone Rose Bowl win in program history.
1995 - obviously the sentimental favorite. Went 10-2, including 8-0 in the Big Ten, to win their first conference title in 60 years, and make their 2nd Rose Bowl trip, where they lost to USC. An early season upset loss to Miami(Ohio) was the other loss. LB Pat Fitzgerald cleaned up on national defensive awards, and RB Darnell Autry finished 4th in the Heisman, but was overshadowed within the conference by Eddie George. Finished #7 in the AP Poll, tying 1936 for a program best.