Here is a great resource on the desert plants of the Southwest United States.
This resource from Tulane University has some great resources for teachers to explain weathering and erosion on a desert landscape.
Desert Biomes — lots of background information about deserts including a great world map that shows some of the distribution of deserts on the earth.
Here is another set of maps that you may want to use to show arid and semiarid deserts.
This site would be ideal for use on an interactive whiteboard. Great images and text that explains about plants, animals, climate and other details of the desert. Great teaching tool created by an elementary education student at Boston University.