[Linderpat]

I just moved back to Pittsburgh from Bozeman MT. I have made the trek cross country a number of times, including in two Porsches and two Mustangs. It is a great ride. My advice, skip the south route on I-15 and I-70. Yes it's pretty for a bit (but only to Denver), but it is just as pretty and far more so if you stay on I-90 all the way through.
You'll see tons of cool stuff in Montana, and at Bozeman, it is a short hop down to Yellowstone and Grand Teton. Then come back up through Yellowstone, thru Lamar Valley (the Serengetti of north America), out thru the northeast exit to Cook City and over the Beartooth Pass - the single most spectacular road in the US. Go thru the little town of Red Lodge, back up thru Billings and onto the 90 again, then keep going East. You'll go thru Rapid City where you can see Mt Rushmore and the other sites nearby, like Devil's Tower and the Crazy Horse memorial being carved into the mountain. Just keep going accross the 90 thru the rolling upper plains, and see hundreds of cool giant windmill farms and beautiful vistas. In SD, you'll see where Dances with Wolves was filmed. Hit Chicago for a stop there - great city, then push on home.
This will be a much better ride than what you'll get taking I-70 accross CO, Nebraska, KS, etc. Those are forever long, boring and perfectly flat. Plus, the I-90 drive will allow you to drive pretty much as fast as you want all the way to Wisconsin - I averaged about 100 mph in my sports cars when I went this way - nobody up there. Not the same on the nore heavily travelled I-70 or even I-80 down that way.
No matter, nothing like a good cross country trip to bond with your car. Take and post lots of pics when you do.