Wikipedia
Datasheets.com
DataSheets.com is a large free resource for electronic component datasheets and purchasing information. The website is intended for Design engineers and Electronics purchasing agents. DataSheets.com was developed by UBM in conjunction with SiliconExpert Technologies and provides access to 185 million datasheets on electronics components in a database that allows for searching across multiple parameters and methods. Datasheets.com was officially launched on July 18th, 2011.