Those of you that make jewelry might be interested in these two sites I found:

Gemology Online
The World of Gemstones

Why? Because they're big lists of gemstones, complete with little pictures next to each one's name (and big pictures and descriptions in the articles). The Gemology Online site even breaks down gems by color. (And if a gem comes in different colors? It's mentioned in all the relevant color categories.) If you've ever whipped up a gem texture and wanted to know an appropriate name for it beyond "pink" or "orange-yellow", these will probably be useful.