Circuit Diagram http://www.schematics.com/

Elektronik Forum EEWeb
Electronics Forum EEWeb
http://www.eeweb.de/
EEWEb Europe is an online community for electronics and electrical engineers and hobbyists. It offers electrical engineering and electronics forum. It also has electrical and electronic design articles, and resources in the area of RF design, analog design, embedded design, PCB design, test and measure.
Circuit Diagram
http://www.schematics.com
Schematics is the language of electronics. It provides a concise and comprehensive diagrammatic description of a circuit. Schematics.com allows users to connect and share designs and ideas in a like-minded community.
PartSim
http://www.partsim.com
Online Circuit Simulator with SPICE | PartSim