Illustrated Handbook of Succulent Plants: Dicotyledons, Urs Eggli, Springer, 2002. ISBN 3-540-41966-7
Short description and other info on many species, sorted after families. A really good book. The best book I never had.

Illustrated Handbook of Succulent Plants: Monocotyledons, Urs Eggli, Springer, 2002. ISBN 3-540-41692-7
Short description and other info on many species, sorted after families. A really good book. The best book I never had.

Name that Succulent, G. D. Rowley, Stanley Thornes Ltd, 1980. ISBN 0 85950 447 6
Taxonomy, some debatable assumptions. Anyway, a good tool.

Pachyforms: A Guide to Growing Caudiciform and Pachycaul Plants, Philippe de Vosjoli, Advanced Visions Inc, Vista, CA, 2004. ISBN 10: 0974297118+9.
Great inspiration and information.

Plant, Janet Marinelli, DK / KEW, 2004, ISBN 0-7513-4797-3
A reference book on all kind of plants, explaining not only how to care, but also why. Great photos, mine on page 103.

Socotra, The Lost Island, Alain Christophe,  Cactus & Co
Great photos from a Socotra tour, with some information on the plants.

The World Encyclopaedia of Cacti & Succulents, M. Anderson, Hermes House, 2002. ISBN 1 84309 355 3
Not that many plants, but easy to look-up in, and simple easy info. Good photos.