Need some places to sight see on our Trip, any help?

My GF and I are going from Bozeman, MT to Orlando, FL and we'd like a few places to stop along the way....make a little vacation out of the treacherous drive. We're heading immediately south (to avoid snow issues) to Las Vegas so we can go by the Hoover Dam and then we're heading east and will make a detour to the grand canyon. After that, i'm open to suggestions: It looks like we'll be on I-40 most of the way, so anything along there would be nice, thanks!