http://webmineral.com/ An Excellent on-line Mineral Database.
http://www.mindat.org/ Another very good on-line Mineral Database
http://www.nhm.org/research/minsci/exhibits.htm Natural History Museum: Los Angeles; Mineralogy Section...really worthwhile if you are visiting the Los Angeles area.
http://bancroft.geol.ucsb.edu/ The Bancroft Mineral Collection at the University of California at Santa Barbara. . . at entrance of Geological Sciences Dept.. must see if you are in Santa Barbara; otherwise look at pictures of its minerals on this excellent site.
http://www.lrz-muenchen.de/~Mineralogische.Staatssammlung/Arbeitskreis.htm Prominent Mineral Organisations in Germany: some in English.
http://www.minrec.org/ Mineralogical Record
http://www.rocksandminerals.org Rocks and Minerals Magazine
http://www.crystal-mine.com The Crystal Mine, by Jack Crowley
http://www.palagems.com Pala International; gemstones & jewellery
http://www.douglassminerals.com Douglass Minerals
http://www.lehighminerals.com Lehigh Minerals & Fossils
http://sunnywood.com Sunnywood Collection
http://www.keysminerals.com Kiyoshi and Erico Kiikuni of Japan
http://www.alpine-minerals.de Alpine Minerals, Germany, outstanding colorful Minerals by Gerd Wiedenbeck
http://www.directoryscience.com Directory Science is an excellent Compehensive Science Directory
http://www.the-vug.com/ A venue for finding all kinds of mineral-related topics
http://perso.wanadoo.fr/rare.microminerals/ A wonderful web-site for carefully identified Micromounts