Nominet UK
Nominet sets standards and has information about web domains including who owns them and which ones are available. It also gives awards for good practice.
Nominet

Google Analytics
For free analysis of your website traffic
Google analytics

World Wide Web consortium
The body which establishes standards for web usability and the quality of code.
WWW3

Look up file formats
If you wonder about a file you've been sent look it up here
Almost every file format in the world!

Look up meanings of words
An online reference dictionary
Oxford Dictionary