Here are some helpful links with information about stones and gems:

Gemstone Meanings

Healing Stone Database Search

Avalon Crystals

The Meaning of Healing Crystals

Peaceful Mind: Alternative medicine and therapies for healing mind, body, spirit

Beads for Prayer: Gemstones Enhance the Power of Prayer

Gemstones & Their Meaning

Some basic stone information can found in these books:

The Crystal Bible
by Judy Hall
Walking Stick Press

Stone Power
by Dorothee L. Mella.
Warner Books

Crystal, Gem & Metal Magic
by Scott Cunningham.
Llewellyn Publications