Simulation and design tools - 

  • Circuit lab - Free Online tool to sketch, simulate, and share schematic. We use the same for our site.
  • Fritzing - Open source hardware initiative for schematics and PCB layout..
  • Partsim – Free online circuit simulator with spice.
  • WebSim - A Simulation-Based Online Electronic Circuits Laboratory (MIT OCW).

Electronics projects/circuits/schematics - 

  • Build Circuit – Lots of LDR projects.
  • ElectroSchematics - Discover circuit designs, basic electronics ideas, circuit wiring, kits.
  • Electrosome - Electronics Projects and Tutorials
  • Electronics 2000 – for electronics hobbyists, engineers and students. Online calculators, software downloads, technical data, beginners guide, pinouts, forum, links and more!
  •  DIY Electronics Projects - DIY Electronics Projects, Circuits Diagrams, Hacks Mods, Gadgets and Gizmos.
  • Electronics Projects:Get 100% output guaranteed electronics projects like embedded, electrical, robotics, sensor based and more electronics related projects for engineering students.
  • Open Electronics - Open source electronics projects.
  • Electronics Hub: One of the best blogs in electronics for engineering students and professionals which provides good information on various electronics circuits, projects ideas, block diagrams, electronics tools, etc. from basic level to advanced level.
  • - This site provides schematics and parts lists of various projects that you can experiment yourself
  • - Electronic Circuits and Projects Forum.
  • – Electronics tutorial and circuits.
  • - Electronics schematics diagram
  • 555 Timer Circuits - All the electronics info you need to know about the 555 Timer.
  • - Electronic Tutorials, Electronic Project Kits, Robotics Guide for Students, Amateur and Professionals. Computer Architecture and Digital Circuits.
  • - A resource containing a collection of  30,000+ electronic circuits or electronic schematics cross-referenced into 550+ categories.
  • - Numerous tested circuits of all types for beginners to advanced levels.
  • - A site for ASIC/DIGITAL beginners

Educational sites -

Online arduino tutorials/projects -