ARRL - The national association for Amateur Radio
Slashdot - Tech. News
NewsForge - Linux/OpenSource online Newspaper
Linux
The Linux Kernel ArchivesDistroWatch - Linux distribution info
SAMBA - Windows, Linux networking
KDE - K Desktop Environment
LinuxQuestions - Linux help forum
Server
Apache - Open Source Web Server and other Web Server softwarePHP - Web Scripting Language
MySQL - The World's most popular open source database
Programming
Sourceforge - world's largest Open Source software development website
Freshmeat.net - Open Source software development website (not as large as sourceforge)
Ruby - CrossPlatform and Internet Scripting Language
Ruby Central - web resource for everything to do with the Ruby language
RubyForge - open source Ruby projects
Other
Maxim ICMicrochip - PICmicro Microcontroller
Parallax - Home of the Basic Stamp Microcontroller
CrustCrawler - Robotic Design & Development
Lynxmotion - robot kits and components