I havent' done it myself, but a friend of mine that I know used to do long haul in that stretch of the country, so I'll relay his findings
Chicago has to be a stop on your journey, especially if youre' a sports fan. Being the only four sports town on your route outside of Detroit, there's guarenteed to be a game playing whenever you decide to drive through. And the cuisine? Deliciso! Stopping by Giordanos's should be on your itinerary, for starters. Pretty much you coudl book a whole day or two and it wouldn't be wasted in the Windy City.
Also heard good things about Seattle. The sports scene is decent (I'm told the new park that the Mariners have is leagues ahead of the Kingdome), and there's a reason why they're known for coffee.
There's also Yellowstone Park if you're into that sort of thing. It's a nice break from the road, and is about an hour or so off the I-90 near Bozeman.
Outside of those and Mount Rushmore though, there's not a heck of a lot to see or do between Chicago and Seattle. It's just miles and miles of prairie and then mountains, which are great for viewing, but if you're' going after November lose their appeal quick when the snows hit.