I would add Kane Creek. This is one of my favorites. A little of everything. Moderate with only a couple of technical spots. But you can run in the creek wash and end up on rocks.
Flat Pass (Steelbender) is a good trail to test your ability. If you can do that one, you can pretty much do anything out there. It is an 11 mile trail out of town (or into town) depending on which way to enter it. But you can get lost on this one easily if you are not careful.
A good day loop would be Poison Spider, Gold Bar Rim and Golden Spike. But you would have to take the highway South back into town for about 9 miles. Not a problem if you are plated.
The slickrock trails (Slickrock, Poison Spider and Golden Spike) are pretty well marked so you don't lose your way.
Amasa Back ends up on a 1000 foot cliff and has some good size steps to climb out of. There is Yellow Hill on Prichett that is a must to climb up if you want a challenge. And like Rod said, for a real challenge, take the single track at the end of Porcupine Rim. It does have some drop offs that will give you a case of the willies. You can make it down to the road and back west into town but at the end, there are 3 foot steps you will need to walk down.
A great place to ride. If you have never been there, it is a great place for trucks too.
If you want, below is a link to the pictures of Moab trails over the past 3 years.
http://albums.photopoint.com/j/AlbumIndex?u=1600327&a=12204751
[This message has been edited by Dougie (edited 04-02-2001).]