Most of the good stuff is listed above. For a different view, speed past Hoover Dam to Kingman, then take US93 toward Wickenburg and slow down. Some miles past Wikieup, take AZ97 and AZ96 east past Bagdad, and AZ89 north to Prescott. This whole route crosses some of the most splendid High Mohave terrain (and I've been wandering the Mohave for 5+ decades). From historic Prescott, don't miss vertical Jerome and red-rock Sedona and fabulous Oak Creek Canyon via AZ89A. I'm selling my historic adobe house on the Mexican border; if I were staying in Arizona, I'd move to Prescott (and not just because I have a sister there).
If you visit Zion, go north just a little to Cedar Breaks Nat.Mon. Be sure to take an oxygen mask; that's HIGH country. Wander around the Markagunt Plateau between Cedar Breaks and Panguitch and Hatch. Roll down to Kanab and maybe to Jacob Lake. (North Rim of the Grand Canyon is inaccessible till around Memorial Day.) Eyeball the polygamists' huge houses around Colorado City, south of Zion. West of Zion, UT18 north of St George runs through splendid joshua-tree country. Then cut back west to Panaca and Caliente (see below).
Originally posted by song_hm Mojave Desert, Nellis Air Force base, Area 51/Racher (if you are into that kind of this - but really, there is not much around to see).
That should be, Area 51 / Rachel. And yes, it's pretty dead there, although the loop through nearby Tempiute is rather picturesque. I've been in Rachel for a couple of fairly major events but those UFO parties just don't happen anymore. And it's a LONG way out there. In that direction, Caliente (pronounced kal-YEN-nee by locals) is more interesting, whether or not a monster cross-desert race is scheduled.