These can be interesting, although not very useful. But many sites post good questions and posters put up intelligent, on-target answers quickly.

Defense Forum
This discussion board covers military topics on global security, war on terror, army, land forces, air force, military aviation, and naval forces, as well as nuclear and missile forces of the world. Users can compare and ask questions about weapons such as fighter aircraft, UAVs, bombers, army vehicles, armored vehicles, tanks, artillery, and war strategy. The site also posts images of new weapons and military vehicles.
www.defencetalk.com/forums

Biomedtalk.com: Biomedical Engineering
This site caters to the biomedical community and has questions relating to a myriad of medical devices, different suppliers, and technologies. Links to other medical forums deal with materials (mostly nanoparticles), dentistry, pharmacology, genetically modified foods, and several other medically-related topics.
www.biomedtalk.com/forumdisplay.php?f=40

Mechanical Engineers-Welcome
Billed as a place for mechanical engineers to share technical thoughts, info, subjects, related posts, fun, and so forth.
http://www.facebook.com/MechanicalEngineersWelcome

Engineering Tips Forum
Here’s a collection of forums for practically every type of engineer, including automotive, environmental, and packaging. There are also forums on engineering software such as AutoCAD, MATLAB, SolidWorks, and Ansys, as well as career help, engineering standards, GD&T, and project management. It seems like this meta forum lives up to its motto, “Smart questions, Smart answers, Smart people,” with at least one answer, more like three or four, for every query submitted.
www.eng-tips.com

Mechanical Design Forum
This U. K. site covers all aspects of mechanical design, including industrial design, news items and events of interest to mechanical designers, manufacturing, and even suppliers. There’s also a section on CAD software and the business aspects of intellectual property protection.
http://tinyurl.com/bw7ss8b

IEEE Women in Engineering
IEEE Women in Engineering (WIE) is the largest international professional organization for women engineers and scientists.
http://www.facebook.com/ieeewomeninengineering

Hydraulic Forum
This site has sections for fluid power and hydraulics, and a separate forum for suppliers to post information on current trends and topics in the industry.
forums.hydraulicspneumatics.com/groupee

Mechanical Engineers Rocks
Lots of activity on this page which has a mission to generate confidence in the minds of mechanical engineers so that they can give their best.
http://www.facebook.com/trustmestore#!/MechanicalEngineersRocks?fref=ts

Physics Forum: Engineering
Another meta site that includes forums for electrical, mechanical, electrical, materials & chemical, and nuclear engineering, as well as a general engineering forum. The nuclear forum has some extended discussions of thorium reactors with well-thought-out discussions.
http://tinyurl.com/bt6h4dd

Facebook: Trust Me, I’m an Engineer
A place for all types of engineers and for those who appreciate what engineers do.
http://www.facebook.com/trustmestore