StatSoft

Link:  http://www.statsoft.com/textbook/

StatSoft is a free online statistics textbook.  It covers basic concepts of statistics such as correlations through advanced topics such as quality control charts.  This site is a great reference tool for students taking statistic courses and even management majors who need to use statistics in their field.

Khan Academy

Link: http://www.khanacademy.org/

The website was started by Salman Khan who was tutoring his cousins across the country.  He posted lessons on YouTube so that his cousins would be able to view at their own pace. Khan began receiving feedback from strangers about how useful these videos.  After Khan realized that a lot of people can benefit from his videos, he founded Khan Academy.  This non-profit organization provides over 2,000 videos and tutorials of subjects ranging from grade school biology and mathematics to college level calculus and economics, all of which are free.

Khan discussing about the website at a TED conference: