An online library of AutoCAD, Viz, and 3DStudie blocks of varions manufacturers, with drag and drop feature into i-drop enabled programs [requires IE]. http://www.autodrop.net/
A library of isometric drawings for use with AutoCAD and other CAD drafting software. Subject areas include piping, power transmission, electric motors, plumbing, tubing, and HVAC. http://www.isoblocks.com/