UsingEnglish.com

This is a very useful tool in language references. As the proper website describes it, it is an “English language reference including definitions of English grammar terms, irregular verbs, phrasal verbs and idioms. Also includes links to online dictionaries.”
Bibliography:
http://www.usingenglish.com/reference.html

The Python Language Reference

This reference manual describes the syntax and “core semantics” of the language. It is terse, but attempts to be exact and complete. The semantics of non-essential built-in object types and of the built-in functions and modules are described in The Python Standard Library.
Bibliography:
http://docs.python.org/reference/

Dublin Core

The Dublin Core is a model of metadata managed by the DCMI (Dublin Core Metadata Initiative).
The Dublin Core Metadata Element Set (DCMES) consists of 15 metadata elements, which are optional, can be repeated or appear in any order:
1. Title
2. Creator
3. Subject
4. Description
5. Publisher
6. Contributor
7. Date
8. Type
9. Format
10. Identifier
11. Source
12. Language
13. Relation
14. Coverage
15. Rights
It is [...]

Corpus Linguistics

I have chosen this language reference based on Google Scholar automatic searching. This work has been quoted 698 times and when you click on it opens a PDF file where you can check that.
It consist on Corpus Linguistics written by Tony McEnery and Andrew Wilson (Lancaster University) Edinburgh: Edinburgh University Press (Edinburgh [...]

Del.icio.us

Del.icio.us is a social bookmarking web service for storing, sharing, and discovering web bookmarks. The site was founded by Joshua Schachter in late 2003 and acquired by Yahoo! in 2005. It has more than three million users and 100 million bookmarked URLs.
Its social bookmarks manager allows to attach the sites you visit to your del.icio.us [...]

ELRA

ELRA (European Language Resources Association) stands for The European Language Resources. The ELRA official page tells us, ELRA “is the driving force to make available the language resources for language engineering and to evaluate language engineering technologies”. This means that it makes easier for European or non-European organizations to have language resources and to evaluate [...]