We did Zion recently, and honestly, was not very impressed; it was very busy, crowded, and the views were just OK compared to Arches... I would rather have done Bryce. We also did Moab/Arches, which was great, and want to go back to spend more time there.
We stayed in Williams during the Grand Canyon segment of our trip, and visited Bearizona, it's a cool little drive through zoo, with bears, buffalo, wolves and more, just roaming around. It's fairly new, and is not quite finished yet, but it was a great stop. We liked Williams itself as well, neat stores and cafes/restaurants.
Edit: Oh yea, I forgot to add Sedona :S... that's very well worth seeing as well.
