JavaScript:
The JavaScript Guide from MDN: https://developer.mozilla.org/en/JavaScript/Guide
The JavaScript Reference from MDN: https://developer.mozilla.org/en/JavaScript/Reference
Eloquent JavaScript: http://eloquentjavascript.net/
An index to some good JavaScript content at QuirksMode: http://www.quirksmode.org/js/contents.html
Essential JavaScript And jQuery Design Patterns: http://addyosmani.com/blog/essentialjsdesignpatterns/
jQuery Fundamentals: http://jqfundamentals.com/book/index.html
Node.js:
The Node Beginner Book: http://www.nodebeginner.org/
Hands-On Node.js - Not free, but the 60 page demo is good enough to convince me to buy this as my next eBook: http://nodetuts.com/handson-nodejs-book.html
NodeTuts - A series of Node.js tutorials: http://nodetuts.com/index.html
HTML5:
Dive into HTML5: http://diveintohtml5.org/
HTML5 Doctor Archive: http://html5doctor.com/article-archive/
Security:
Electronics:
Netduino:
The main Netduino website: http://www.netduino.com/
The Netduino forums: http://forums.netduino.com/
Beginner's Guide to C# and .NET Micro Framework: http://wiki.tinyclr.com/index.php?title=Category:Beginner_Guide_ebook
Python:
Think Python: How to think like a computer scientist: http://www.greenteapress.com/thinkpython/thinkpython.html
