The best, most inexpensive one for non-cactus succulents is, without a doubt, the one from Fred Dotort.

http://www.timberpress.com/books/timber_press_guide_succulent_plants_world/dortort/9780881929959

Great cultural information too.

You might check to see what your local library has, then purchase if you find something you like.

Check abe.com (used book site) for a better price on the one cactuscharris mentioned. Possibly used.

I have Succulent Flora of Southern Africa by Doreen Court, which has served me well, since most of my succulents are from South Africa. I have also noticed that if you buy a book about Cacti and Succulents, 90% of it will be cacti.

Thanks!

I found one I like at the library today: "The Complete Illustrated Guide to Growing Cacti & Succulents" by Miles Anderson. It won't list every succulent, but it has sections on the major groups, care section in the back of the book.