These are some of the best and most useful sites that I have used time and time again, click on the link below each short description, you will soon sort out the ones that do it for you.
This is an online textbook that covers just about all business and management issues
Another good source of ‘bite sized’ theory
The Art of War
Organisational Management link
CSR Corporate Social Responsibility http://www.btplc.com/Societyandenvironment/CSRresources/CSRBasics.pdf
More models and theories than you can shake a stick at
The daddy of business, management and development resources