RCMAN46: I could not agree more, although I would add a good 4-5 day backpack trip to that list. I've walked into some areas where not even a horse would've been able to trek. I look forward to the day when I'm retired and am able to hike the ENTIRE Idaho Centennial Trail in one shot. Some 600-700 miles, will take me 3-4 months. Hopefully my knees are still in good working condition at that time!
ejfranz: How old is your daughter?
A few more locations came to mind this afternoon...
Lots of places to pull off US12 and watch the river and just generally take it all in. Don't be in too much of a rush to drive thru this 50mph corridor. Maybe consider a drive up the Selway Road.
Yankee Fork, only about 20 miles from Stanley: a very cool area, and touring the old dredge is a must if you make it. It is humbling, even depressing to see how that single machine literally turned the valley upside down in its search for gold. And while you're in the area, a walk thru the old ghost town of Custer is pretty neat.
EBR nuclear reactor, about 20 miles from Arco: the world's first nuclear reactor that generated electricity.
In addition to Redfish Lake, there are a few more lakes on the west side of the Stanley basin worth checking out if you have time: Alturas, Pettit, Yellow Belly.
Hell's Canyon, if you can swing it. I normally drive into the canyon from Cambridge and drive the road all the way down to Hell's Canyon Dam where it dead-end's. But I've heard that seeing the canyon via jet boat traveling upstream from Lewiston (as was mentioned above) is also very cool.