LAW's Custom Ponies

If you are interested in learning more about how to make custom My Little Ponies or about the collecting community, the links below may help you.

Forums

My Little Pony Arena - A collectors' forum which includes a very active customs section
My Little Pony Trading Post - A collectors' forum which includes a section on tutorials

Hasbro Toy Shop - They sell a "Decorate Your Own" pony that is blank white and only available online. This is a great way to get started customizing.
Aves Studio - The makers of apoxie sculpt.
Embellishment Village - The makers of Angelina Film and Fibers. These are only available online.
Joann Fabrics - They stock Angelina Film and Fibers in their online store, but I have never seen them offline.
Dollyhair.com - Sells several types of hair and rehairing tools.
My Little Customs - Sells wings, hair, mermaid bubbles, and other supplies. This is also a good source of tutorials.