MSDN Library

http://msdn.microsoft.com/en-us/library/ms123401.aspx

Resources from Microsoft for:
Web development
Game development
Phone development
Cloud development
Data development
Desktop development
Programming languages

Features:
Code samples
Walkthroughs
Articles

Writing for Engineering and Science Students

http://www.writing.engr.psu.edu/

Writing guidelines for eng and sci students.

Features:

Resources from good universities
Exercises
Articles

Pink Monkey Notes

http://www.pinkmonkey.com/index2.asp

Free literature summeries and notes, similar to SparkNotes but not so branded. Only covers literature and books.

SparkNotes

http://www.sparknotes.com/sparknotes/

Articles and study help about everything. Best known for their literature notes, but their other stuff is pretty great. Can get distracted by the non-academic related articles but you should be fine if you stay in the academic pat of the site.

Features:
College resources:
- College reviews
- College video tours
- General college articles
Articles:
- 25+ subjects, in depth coverage
- Famous SparkNotes Lit. guides
- Famous "No Fear" Lit. series including Shakespere and other classics

Purdue Online Writing Lab

http://owl.english.purdue.edu/

Subjects:

Writing
English as a second language
Job search and professional writing
Research
Style and grammar

Features:

Exercises
Guides
Articles
Teacher and tutor resources

Life Write

http://www.lifewrite.com/html/class.htm

Free online writing course by an author.

Features:
Assignments
Articles

Hyper History Timeline

http://www.hyperhistory.com/online_n2/History_n2/a.html

Interactive timeline of history: "Over 2000 files covering 3000 years of history"

Features: Maps, biographies, catagorization of events by science, politics, religion, war, culture, and time periods, free online textbook and other resources.

Wikiversity

http://en.wikiversity.org/wiki/Wikiversity:Main_Page

Everyone tells you not to go to Wikipedia for information, but we all do anyway. Here's some free educational stuff with liks to even more.

Subjects: Everything
Features: Articles, links, pictures, lesson plans, ordered curriculum, vast amount of topics in each topic.
Amount of resources on site: 17,000+

w3schools

http://w3schools.com/

Subjects:

HTML Tutorials

Learn HTML
Learn HTML5
Learn CSS
Learn CSS3
Learn TCP/IP

Browser Scripting

Learn JavaScript
Learn HTML DOM
Learn DHTML
Learn VBScript
Learn AJAX
Learn jQuery
Learn JSON

XML Tutorials

Learn XML
Learn DTD
Learn XML DOM
Learn XSLT
Learn XPath
Learn XQuery
Learn XLink
Learn XPointer
Learn Schema
Learn XSL-FO
Learn SVG

Server Scripting

Learn SQL
Learn ASP
Learn ADO
Learn PHP
Learn ASP.NET
Learn Razor
Learn .NET Mobile

Web Services

Learn Web Services
Learn WSDL
Learn SOAP
Learn RSS
Learn RDF

Web Building

Web Building
Web Browsers
Web Certification
Web Hosting
Web W3C
Web Quality
Web Semantic

Features:
- Quizzes
- Articles
- Tutorials
- Editor, see browser results

Free Math Help.com

http://www.freemathhelp.com/

Math help website for high school math.

Subjects covered:
Algebra
Trigonometry
Calculus
Geometry
Statistics

Features:
- Active message help board for questions
- Lots of atricles on math
- Misc articles on things like calculator buying, finance, etc.