IMA – The International Mineralogical Association.This is the group that approves new mineral species through their Commission on New Minerals and Mineral Names.
Mindat.org – An exhaustive online Wiki for mineral data. This site contains up to date information and data on all mineral species, synonyms, and locations. Mindat.org also host discussion forums and mineral-related news like new discoveries or show dates.
Mineral Database – Database of 4700+ mineral species; many photos; Dana, Strunz, and chemical classification listings; and pronunciation guides.
RRUFF has an extensive database of Raman spectroscopy, X-ray diffraction, and chemistry of minerals.