U.S. EPA's compilation of water-saving plant lists: http://www.epa.gov/watersense/outdoor/what_to_plant.html (use drop-down menu to choose state-specific information)
The Tucson region native and low-water-use plant list: http://wrrc.arizona.edu/sites/wrrc.arizona.edu/files/Tucson%20AMA%20Plant%20List.pdf
Brad Lancaster's drylands plant lists: http://www.harvestingrainwater.com/tucson-az-plant-lists/