Dictionaries, Glossaries, Lexicons et al
The Internet Search Tutorial for translators, by Manon Bergeron and Manten van Steenbergen. This short course teaches techniques that may allow you to limit your use of dictionary resources. Worth reading. Using these tips in conjunction with the Copernic program (see Favorite Tools, below) is an extremely powerful and effective way of searching the net.
Encyclopaedia Britannica: sometimes you just need some more background (E)
Eurodicautom: produced by the European Commission (multi-lingual).
Go to "Database Review" under Web Search Companion for tips on Eurodicautom use provided by Manten van Steenbergen.
European Commission: other language aids produced by the E.C. (English style guides)
Financial:  very impressive terminological resource by Manon Bergeron (mainly F <> E)
Grand Dictionnaire: produced by the Office de la langue française, Quebec (F <> E)
Industry portal site: multi-industry (E)
U. de Sherbrooke index site for dictionaries et al.: comprehensive (multi-lingual, mainly F& E)

Geoscience & Engineering
Ryerson University GIS index site: (mostly English)
Oklahoma State U., Geotechnical Virtual Index: (mostly English)

Mining & Minerals
American Geological Institute (E)
American Petroleum Institute (E)
Canadian Minerals Yearbook (E/F)
Mining Technology (E)

Standards and Specifications
American National Standards Institute (E)
American Society for Testing and Materials (E)
Canadian Standards Association (E/F)
Institute of Electrical and Electronics Engineers (E)
Favorite Tools
Copernic searchware: (light version available at no charge)
Wish you could search 15 or more search engines at a time? Wish you knew of specialized search engines for a very particular search? Download the light version and you may just never use another plain-vanilla search engine again!

Termium terminology database:
Not free, but this Government of Canada-produced French <> English database (available as a CD-ROM or an on-line subscription) is invaluable for those of us who work with the federal government. Otherwise, it's simply an excellent French <> English resource, covering many sci-tech areas quite well.  Do you have yours, yet?

Sci-Tech Translation colleagues (other languages)

Ursula Vielkind: English <> German
Michael Rudy: English <> Russian, Ukranian
Volodymyr Goncharov, Engineering Translation Service: English > Russian