Explains analysis of stress and strain, strength, etc in soils with good visual diagrams: http://environment.uwe.ac.uk/geocal/SoilMech/basic/soilbasi.htm
An interactive site that explains how dams crack and the forces that interact with dams http://simscience.org/cracks/index.html
Shows mohr circles for common stress states, how to, etc.
http://www.tech.plym.ac.uk/sme/mfrg315/mohrc1.htm
http://www.ijee.dit.ie/OnlinePapers/Interactive/Philpot/mohr_learning_tool.htm
Fantastic website that covers all aspects of the all important Mohr's circle. Has interactive tutorial style questions and great explanations and visual representations. Highly recomended
http://www.doitpoms.ac.uk/tlplib/metal-forming-1/printall.php
Mohr's circle explained in much depth.