American Society of Mechanical Engineers. Has a useful discussion area, but you have to be a member to post a question.

Institution of Mechanical Engineers (UK). Look in the library section for an extensive directory of engineering resources.

MPIF / Metal Powder Industries Federation. Comprehensive resource for information about powder metallurgy (P/M) and particulate materials. Details about the process and technology, design data and applications, resources for technical publications, standards, conferences, and seminars, information on the P/M industry and companies.

National Society of Professional Engineers. The organization provides a digest of important engineering press articles from a wide range of periodicals and a discussion group for members.

Precision Metalforming Association. The site includes an extensive supplier directory and a forum for members.

Society of Manufacturing Engineers (SME). A deep site with good archives.