Virtually anything can be used to create a mobile. I have used quite a variety of different materials over the years, which include:

Metals - Steel, copper, brass, aluminum, and tin.
Paper - Cardboard, construction paper, and tissue paper.
Plastic - Formed, molded, sheet, liquid, and recycled scrap.
Wood - Balsa, driftwood, and various formed pieces.
Recycled materials - Computer chips, film caps, CDs, glass, etc.
Finishing touches - Paint, fixers, coatings, hanging hardware, etc.

The materials I use tend to work with me as much as I work with them. That is to say that, as I work with them, natural forms emerge, allowing a natural partnering of form and function... of natural evolution and artistic vision.