Analog and Digital semiconductor manufacturer; source of data sheets and application notes.
http://www.analog.com/support/Design_Support.html
Application Notes from Fluke. Registration required.
http://www.fluke.com/support/s_appnotes.asp?agid=29&sid=216
Transformers, reactors, coils, custom, technical information and links.
http://www.yesmec.com/technical/index.html
How to measure practically any quantity, electrically.
http://www.picotech.com/measure.html
Application notes on power systems.
http://pm.geindustrial.com/faq/Faq.asp
Analog, digital, RF, Audio, discretes and any other part you can think of. Data sheets, and application notes.
http://mot-sps.com/
High performance analog integrated circuits primarily for the video, optical storage, DC/DC converters and XDSL.
http://www.elantec.com/pages/app_notes.html
Mostly discrete semiconductors application notes.
http://www.microsemi.com/support/micnotes.asp?MN=316