Online Electronics Tutorials and Books
 General electronics theory
Electronics Club Great set of tutorials for beginners. You can find basics about electronics components, logic circuits, projects and so on...
All About Circuits Online version of the great free ebook by Tony R. Kuphaldt, highly recommended!
The Resistor Guide Online reference on all resistive elements, such as resistors, potentiometers, varistors, thermistors and more.
 Soldering and practical skills
 PCB layout and CAD
Hitex insider guidesGuides for several ARM based MCUs
 Programming languages
 FPGAs and hardware description languages
 RF design
Untitled site with easy to understand information on RF design and a large range of experiments. [as of 03/21/15 this site is down]