Big Road Trip: What should I not miss?

My buddy and I are going to travel to Denver in early June. We have to be in Sacramento the second week in July and back to PA at the end of July. We are hoping to see Yellowstone for a couple days, Grand Canyon for a couple days, and Yosemite for a couple days. We are talking about a day or so in North-Western Mexico. We are going to Crater Lake and Seattle after Sacramento, then to Glacier National Park, Mount Rushmore, Badlands, on the way home. What are some "Don't Miss" things to see that maybe people don't know about. We are a little adventerous, but not too adventurous.
Any ideas would be appreciated. Thanks

Regulars here probably get sick of reading me say this but since you're going right past it on your way to Seattle, you must stop at Mt. St. Helens. Since the cataclysmic blast of 1980, nature has done a rather amazing job restoring itself. Yet there are still areas where the devestation is mind-boggling. If I was to stop to see only one thing in Washington state, that would be it.

If you have more time, the Olympic National Park on the peninsula is the only temperate rain-forest in the United States and has spectacular scenery. The Trail of Mosses in the Hoh River Valley near Forks, WA, is one of the most magical places I've ever been. But there are numerous other sites worth stopping at around the peninsula as well and would be a great 2-day detour.

Of course, Mt. Rainier is also amazing. While the mountain is not the tallest in the US, its mass is awesome to see. And their are more glaciers on "The Mountain" (as we call it here) than there are in Glacier National Park.

To be honest, Crater Lake is amazingly beautiful but, if time is short, Crater Lake will probably always be there but Mt. St. Helens won't. At least not in its present state as it is always changing with nature's renewal. I go every year or two and always regret not going more often in order to witness the rebirth of this area.

Hope this gives you some good ideas.