I see the thread is over two years old, but I might as well offer some input.
Up in NW Indiana there are some pretty roads to be driven. Dune state highway between Gary and Michigan city is beautiful from late Spring to Early Fall (Think tunnel of green). Lots of nice pleasant/pretty drives around the dunes. If you want some more rural roads with some nice scenery, down around Crown Point and the areas south or Highland are pretty. It's nasty up around Gary and East Chicago/Hammond, but only 10 miles or so to the south and it starts to get really nice. I used to drive all over NW Indiana while I lived up there because I had nothing better to do on my days off.
The drive between Indianapolis and French Lick (as Google maps it) is sleepy until you're about 20 miles from the West Baden resort. Then, it gets very twisty, hilly, and beautiful too. I'd bet October is a fine month to go when the leaves are turning. Winter would be a blast too if you had a good set of snow rubber.