W3Schools - A collection of free HTML, CSS, JavaScript, DHTML, XML, XHTML, WAP, ASP, SQL tutorials with lots of working examples and source code.
SourceForge - the world's largest Open Source software development web site
Science & Technology
Nature - "... publishes the finest peer-reviewed research in all fields of science and technology..."
MIT OpenCourseWare - "... a free and open educational resource (OER) for educators, students, and self-learners around the world"
ElectronicDesign - The premier independent information source for electronics engineers, programmers and designers
Useful Software
Windows Utilities
FreeFileSync - Great tool for file/folder synchronization, with many uses, such as keeping a portable drive and system drive in sync, making backups, comparing the contents of directory structures, etc.
V - The File Viewer - Inspect and manipulate directories and files, very fast, many capabilities.
Process Explorer - For Windows, an advanced process management utility that picks up where Task Manager leaves off.