The Salt is a nice class 3-4 run, mostly 3. Permits are required from both the forrest service and the indians.
You can do anything from a half-day trip to a 5+ day trip. Full length is like 56 miles.
What I like about the Salt is it is one of the last free-flowing rivers. It, and its side creeks, drain a huge area. The salt has hit 220,000cfs. A side creek called Canyon Creek has hit over 50,000cfs.
The downside to this is that once the run-off is gone the water drops to almost nothing.
Because of its free-flowing nature, the Salt has huge pristine white sand beaches. Just watch out for camping on one of these in a windstorm.
Since that asshole Taz Stoner dynamited Quartzite (presumably under orders from Pat Blum) rapid (used to be a 5+) the run has seen an influx of "Arizona Geek Boaters". That portage used to keep all but the highly adventurous out of the canyon.
The run is extremely scenic and offers numerous indian ruins to explore. Cherry Creek is one of my favorite places to lay over. The Maze and Blackrock are fun rapids. And there is nice surfing everywhere depending on water level.