The Human-Languages Page, by Tyler Chambers, has links to nearly 2000 language-related web sites, including a few hundred glossaries. The Translator's Home Companion at Language Automation, Inc. also has hundreds of glossaries, sorted by language or by subject. Babylon.com has glossaries of many subjects in multiple languages.
There have been many great software localization projects in the past, usually specific to a particular computer language or operating system. Their glossaries are also valuable references for Internet and Web. The Microsoft glossaries are standard tools in most software localizer toolkits. Also take a look at Apple, SGI, and Sun. There are language-specific localization tools for Perl, for C, and for Java.
Frank Dietz' web page has a non-searchable listing of 1500 glossaries.
Cecilia Falk offers a Language Links page.
Gabe Bokor's List of Glossaries and Dictionaries at Translation Journal