[MATH] Eric Weisstein's World of Mathematics

MathWorld "is a comprehensive and interactive mathematics encyclopedia intended for students, educators, math enthusiasts, and researchers". Numerous topics including Algebra, Applied Mathematics, Calculus and Analysis, Probability and Statistics are clearly explained with references included for further exploration. You can find the newly incorporated and updated materials on the site via Headline News (RSS) and New in Mathworld. In addition, animated GIFs and java applets are provided in Interactive Entries.