University of Wisconsin - Eau Claire
This is a commercial site with a huge range of information on spreadsheets in general and Excel in particular. It also has links to many other sources of spreadsheet information.
Teach-ICT: no registration is needed.
ALISON: Registration is required.
This site contains a huge range of definitions, including Every File Extension in the World.
Another major computer terms definition site
IT Services Short Courses Home Page
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