There is, to our surprise, quite a few books about cacti and succulents; including ones with beautiful pictures.
In South Africa some of the books are available in the shops of the botanical gardens of the National Botanical Institute, others are available at bookshops (or they can order them for you) and there is also the possibility of mail-order. Silverhill Seeds and Umdaus Press both have a list of succulent related literature which I left out of the list below.
Books of interest (both for beginner and advanced succulent gardeners) are:
‘Cacti, the compact study guide and identifier’ by Charles Glass and others. ISBN 0-7858-373-4
‘Gardening with succulents’ by Prof. Gideon Smith. ISBN 1 77007 082 6
‘Vetplante van Suid Afrika’ by Ernst van Jaarsveld and others. ISBN 0 624 03901 3
‘Succulents, the new illustrated dictionary’ by Maurizio Sajeva & Mariangela Costanzo. ISBN 0-88192-449-0
‘The illustrated encyclopedia of cacti’ by Clive Innes & Charles Glass. ISBN 0-7858-1358-6
‘Cacti & Succulents’ by Hans Hecht. ISBN 0-8069-0548-4
‘The complete book of cacti & succulents’ by Terry Hewitt. ISBN 0-7894-1657-3 (this was our first book on the subject)
‘Guide to the aloes of South Africa’ by B. van Wyk & G. Smith. ISBN 1 875093 41 9
‘Mesembs of the world’ by Gideon F. Smith & others. ISBN 1 875093 13 3
‘The cactus family’ by Edward F. Anderson. ISBN 0-88192-498-9
This is just a selection but it gives you something to read for the first few years.