Here is a list of further resources that you might find helpful.

Cacti & Succulents

Connecticut Cactus & Succulent Society: The club I belong to and was President of from 2001-2003.

Growing Tropical Plants in Phoenix: My favorite feature is the ability to look up info about plants by botanical name or common name.

The Genus Echinofossulocactus: A site dedicated to Echinofossulocactus (Stenocactus).

Succulent Euphorbias: A site dedicated to succulent Euphorbias with many photos and growing requirements.

The Amateurs' Digest

The Cactus Mall

Aroids

International Aroid Society: Please consider joining the International Aroid Society. Their web site has lots of information about Amorphophallus, Typhonium, Philodendron, Calladium, Colocasia, Alocasia, and all the other aroids. Membership is cheap and includes a nice newsletter. Click for membership form, you can send a check or use PayPal.