Both auction sites are user friendly and have provided me with some really great stuff. This is a commercial site offering an excellent assortment of really fine mineral specimens complete with color photos. Prices are reasonable and there is an weekly auction of specimens as well. I have several pieces from here in my collection. The Minerals and Mining Page at Albany Stamp Company contains an excellent selection of worldwide rock and mineral postage stamps, including many new issues.
Images are available of some stamps.
Rockhounding Arkansas is an excellent site authored by a fellow geologist. The site provides information on Arkansas minerals and collecting localities, the ins and outs of rock and mineral collecting, and much more. It also outlines the requirements of the Boy Scout Geology Merit Badge and provides reference materials useful for obtaining it. The site contains websites of fellow rockhounds, free classified ads, event and club listings, and much, much more. The Rockhounds Information Page is another non-commercial web site providing useful information for both rockhounds and professionals.