The following sites are worth a visit, I think!

LOCALITIES
Binn-valley	Ate van der Burgt made this fabulous site with all you want to know about the minerals, paragenesis, localities, literature, ...            + many pictures.
Lengenbach	Information about LENGENBACH, the world famous locality in the Binn-valley, Switzerland. With many pictures of the rare minerals from this locality.
Mt.St.Hilaire	Information about Mt.St.HILAIRE, the world famous locality in Quebec, Canada. With many pictures of the rare minerals from this locality.
Franklin	Information about FRANKLIN,  the world famous locality in New Jersey. With many pictures.
Hagendorf	The minrals of the famous phosphate-pegmatite of HAGENDORF, Bavaria, Germany, with perfect descriptions and many nice pictures.
Clara	The minrals of the famous Clara mine near Wolfach in the Black Forest, Germany. With many nice pictures.
SYSTEMATIC
mindat.org	PROBABLY THE BEST THERE IS!! A fabulous source of information !
Webmineral	Information about almost all minerals!
ATHENA	Nice pictures of many minerals!
www.strahlen.org	This is the mineralogy internet site of 'The Strahlen Foundation' (Stichting Strahlen).
mineralen.startpagina.nl/	Dutch site; find everything about minerals in The Netherlands
OTHERS
MKA	The homepage of "MINERANT" in Antwerpen, Belgium. A perfect place to start a quest!
	At "DE BODEMSCHAT" you can buy everything you need for your minerals: books, tools, boxes and very much more!
	The French Association of Micromineralogy. A lot of good information and an international directory of micromounters.
Other collectors	Theo van Loo Jörg Scherber : Fischbachtal (FRG) xls and agates, petrified wood.