A friend passed along this older book to me a few weeks ago and it has REALLY upped my cactus and succulent identification game. While it may be a bit out of date, its photographs allow me to quickly categorize basic types and families of succulents so I can continue my research elsewhere.
My plant ID knowledge is a bit hit and miss, along with my memorization of latin names, but now I have a great resource and a place to start in identifying cactus and succulents that I come upon and photograph.
You can find The Complete Book of Cacti & Succulents by Terry Hewitt on Amazon and quite possibly at your your local library.
You can find even more books on cactus and succulents using this link to Amazon.com, too