Erie Scientific - http://www.eriesci.com/ US

Precision Glass - www.uspg.com

Precision Glass and Optics - www.pgo.com

GM Associates - http://www.gmassoc.com/products/discs_plates.htm

Mark Optics - www.markoptics.com

Valley Design - www.valleydesign.com/

Nanofilm - www.nanofilm.com (not really glass substrates but mask blanks)

Bicron Crystal Products - www.bicron.com (not really substrates either, but other optics related stuff)

Crystal-gmbh - For single crystal LiNbO3 and Quartz substrates at really good prices.

Sydor Optics, Inc. - http://www.sydor.com.
Phone: +1 585-271-7300
Fax: +1 585-271-7309
Contact person: Michael Naselaris (mike@sydor.com)