List Of Useful On-Line Resources: Mostly Mathematics Resources
Videos:
Math and Algebra Help - Videos from MathTV.com
Just Math Tutoring
Khan Academy
MidnightTutor.com Free Online Calculus and Chemistry Tutorials
MIT's Free Online Course Materials: MIT OpenCourseWare (Math OCW)
Example Problems
Main Page - Example Problems
Paul's Online Math Notes
Computer Algebra Systems (Marked with * = download required)
SAGE*
Maxima*
Octave*
Wolfram Alpha
Graphing & Visualizing Mathematics (Marked with * = download required)
Geogebra*: Download optional: There is a web version
GrafEq *
gnuplot *
Gapminder*
Wolfram Demonstrations Project
Interacting with others (Maths chat or whiteboards)
MathIM: A LaTeX web-based chat
MathBin.net - Math pastebin for equation rendering
Dabbleboard - Online whiteboard for drawing & team collaboration - Interactive whiteboard software
Imagination Cubed
I haven't checked all of the resources listed here [there are a lot] but the quality seems good overall, if inclined toward the 'other side of the pond' perspective. There should still be a lot of useful resources here for the UK based institutions.
