Encyclopedia of Earth
Encyclopedia of Earth: Cactus
Describes the physical features of different cacti, the variety of habitats where they can live, their distribution, evolution, taxonomy, and conservation status. (Published: January 10, 2011)
Unite for Literacy
Unite for Literacy: Plants and Food: Great Green Giants
A picture book about a giant cactus called the saguaro. Includes audio narration in nine additional languages with text in English.
PBS
Pbs Learning Media: Deserts
Not all deserts are the same. This still collage produced for Teachers' Domain features views of different deserts around the world.
Missouri Botanical Garden
Missouri Botanical Garden: Plants of the Desert
The Evergreen Project reveals such desert plants as the dragon tree, the saguaro cactus, the prickly pear, the desert spoon, the aloe plant, and the like. Illustrated.
Other
Branimir Gjetvaj: Sonoran Desert, Arizona
This site has several pictures and links on the flora of the Sonoran Desert in Arizona.