I drove past the Apple Dumpling UFO Docking and Teleportation Center on my way down from Zion along route 389 and IMMEDIATELY had to pull a u-turn to check this out. The actual docking station is on private property behind a barbed wire fence, but you can grab some gnarly photos of the center's extraterrestrial visitor and the sophisticated commode, er, command center that is the teleportation device, whose sites are set squarely on Uranus.
As other people mentioned, Silver Reef isn't really an abandoned ghost town considering all the ritzy houses in the surrounding area. It is, however, a fine place to check out if you've got some time on your hands in between Zion and St. George. The museum is supposedly pretty cool, but unfortunately was closed when I drove by. It's free to walk around and explore the area, and $3/person (or $10/family) to take a guided tour.
Grand Staircase-Escalante is a beautiful place to drive through and hike around a bit. The area of the monument is ginormous, so there's everything from forest land to desert and everything in between. Two of the best drives I've ever taken--the Burr Trail from Boulder, Utah and Highway 12 from Boulder into the town of Escalante--were within the national monument.
Best Western/Ruby's Inn effectively has a monopoly on lodging in the Bryce Canyon City, as the whole main stretch of the area is owned by them. The lodging accommodations are fine (if a little overly touristy) and convenient for their proximity to the national park, but if you don't need to stay directly next to the park then I'd recommend finding someplace else to stay in Southern Utah, as it's much easier to find a cheaper and more scenic place to stay not too far away in towns like Tropic or Boulder.
The drive in between Tuba City and Four Corners is pretty barren, but this building filled with graffiti art made the trip worthwhile. You can pull over next to the highway, and walk through the gate in the barbed wire fence. Watch out for broken bottles on the ground and rolling tumbleweed though.
Between Highway 12 and Highway 24, Southern Utah has some of the most beautiful drives I've ever had the joy of making. Highway 12 is known as "Devil's Backbone," and takes you through some rugged and breathtaking territory along Grand Staircase-Escalante on the way to Bryce and Zion. The scenery is amazing, and thankfully there are plenty of pull-offs to snap a picture or 50.
One of the coolest and spookiest places I've ever seen. I heard about the slot canyon from the owner of the Boulder Mesa Restaurant, who gave me directions to find the canyon along the Burr Trail Road. It was incredibly eerie to walk the sandy path in between the canyon walls and hear nothing but dead silence. The trees growing on the canyon floor are totally cool, and give the whole place a very peaceful feel. Take flash flood warnings seriously though, since you do NOT want to be caught in a slot canyon during one.
A great family run place in Boulder. They smoke their meats outside, and the food is delicious, making it well worth the extra minute drive it takes off highway 12. Be sure and ask the owners for directions to the slot canyon in Escalante along the Burr Trail!
Pretty cool place to check out if you've got some time in Boulder, Utah. The museum has a lot of interesting artifacts, but the best part about the park is out back, where you can see the ongoing archaeological dig.
If you have a couple of days in Moab or just want to see something besides Arches or Canyonlands, definitely check out Dead Horse Point. When I first heard that the view was as stunning as any from the Grand Canyon I scoffed, but for real, this place is astounding. You literally walk out of your car at the visitors center parking lot and step onto the edge of this ginormous precipice overlooking the canyon. But be sure and drive all the way past the visitors center parking lot to the Dead Horse Point as well, which offers some incredible views too.