Succulents galore by Evelyn G. at InsiderPages
Once you start collecting succulents, you find out the best places to buy them. Arid Lands Greenhouses is one of the best. You can look over their catalog online and then visit the greenhouse when it's open on Saturday (or make an appointment).
Read more at tucson.citysearch.com
They have a great selection of caudiciforms, Euphorbias, and more.
PROS: Excellent selection of succulents.