Jade's Babblings

I've wanted to take this trip since my parents talked about their cross country honeymoon back in the 70's.

Liam clued me into the fact that i90 goes from Seattle to Boston. How cool is that? I haven't talked to Seth about it yet but it seems like a pretty easy route. And the way we'd be driving it will take us through the following states:
Washington (duh)
A tiny bit of Idaho
Lots of Montana
Some of Wyoming
South Dakota
Minnesota
Wisconsin
Tiny of of Illinois, Indiana and possible Michigan
Onto Ohio, Pennsylvania, and New York
And then arrive in Massachusetts

So.... give me some ideas. What's some fun stuff to do in any of those states? I've found little things that are obvious like zoos and stuff, but I want to find the random things. World's biggest ball of string and stuff like that. I need ideas. We'll have five days to make the trip. Mapquest says it'll take us 44 hours driving straight through so that gives us a few stops to take in the sights. It's 3044.73 miles. That's insane. Glad it's not my car...

Here are some activities I've found so far. They mostly involve parks.
Close Encounters is a cool movie. My parents stopped here. There's lots of silent video of my mom waving.
Idaho falls zoo
wolves are cool
duh
they're bad lands
montana's kind of boring, huh?

The only other resources I'm going off of are routes besides i90, and these two - 1 and 2.

I'm obviously in need of suggestions. Anybody gone cross country before? Have any interesting sites I should check out?