Route planning:
For the Canyonlands National Park area, the park web site has some decent PDF maps showing the roads through the park
http://www.nps.gov/cany/index.htm
Here's a good PDF map:
http://www.nps.gov/cany/planyourvisit/upload/tripmap.pdf
I'd like to suggest that we consider some of the following, which are long "through" trails (i.e., we can go in one way and come out somewhere else - as opposed to an "out-and-back" trail where we go in and come back out the same way):
* White Rim (about 100mi)
* Lockhart Basin
* Devil's Lane/Bobby's Hole/Beef Basin
We could actually do White Rim in a day, but my understanding is it's better to take two and to camp out along the rim.
Lockhart Basin would take us down to the Needles area where we could pick up the West end of Beef Basin and then take it around to the East, or we could catch some other roads that go to the South.
We could also go across the Colorado River into the Maze District, but I don't know that we'll have the time. Maze takes a minimum of 2 days to really do it right.
Note that campsites in the Maze and White Rim have to be reserved ahead of time for the most part.
For the rest of the time, though, as long as we're not in the National Park we should be able to camp pretty much where we want to.
If we stay East of the Colorado, there are a number of areas we can explore South of Canyonlands as we make our way South. I've camped out at Valley of the Gods (just South of Moki Dugway near Mexican Hat) and I can confirm there are lots of good, free campsites there.
Once we cross the San Juan river at Mexican Hat, we'll be on the Rez (Navajo) and AFAIK can only camp in developed (i.e, pay) campsites.
There's a very well developed park at Monument Valley but IMO way too crowded to want to camp there.
That's all I've got for now, I was just glossing over the DeLorme Utah atlas to see what routes there are South of the Needles area and there are quite a few through the La Sal National Forest. This would be South of the Needles and West of US191.
EDIT: Here are some references to the trails I'm talking about:
Devil's Lane
http://www.traildamage.com/trails/index.php?id=294
Beef Basin
http://www.traildamage.com/trails/index.php?id=293
Lockhart Basin
http://www.traildamage.com/trails/index.php?id=96
White Rim
http://www.traildamage.com/trails/index.php?id=138