Mechanical Engineering

American Society of Mechanical Engineers (ASME) (http://www.asme.org)

American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE)  
National Society of Professional Engineers  

Society for Automotive Engineers  

Society of Manufacturing Engineers (SME)  

American Society for Testing and Materials 

Society of Women's Engineers

American Solar Energy Society
 

• iCrank.com: the Mechanical Engineering Portal -- A start page for mechanical engineers that provides a range of design resources. Includes a directory of vendors, covers stock components, custom fabricators, raw materials, and other web directories.  
• imechanica.org -- An online community for people in the international community of applied mechanics hosted at Harvard School of Engineering and Applied Sciences.