Here are some of the places on the web at which you can find useful material about Mathematica and related matters. – The main Wolfram Research site. This is a very large site with lots of information buried away. You can also buy the software here. – A convenient place to purchase the software in the UK.

news://comp.soft-sys.math.mathematica – A news group dedicated to Mathematica. If you post a problem here, you are very likely to get a solution from someone at WRI, or from another Mathematica user. – The home page of "Live Graphics 3D" – a free 'must have' application for anyone involved in 3-D geometry or plotting. It displays 3-dimentional Mathematica objects in OpenGL so that they can be rotated in real-time. To achieve speed, the shading has to be fairly crude, but it also has an option to generate PovRay output (ready for ray tracing). – A source of more Mathathematica tips and Ted Ersek's Supplementary Help browser. – David Park's Mathematica site, with lots of Mathematica applications in physics. – A free maths encyclopedia run by Eric Weisstein at Wolfram Research. This is an absolute treasure trove of information, mostly written to be accessible to the largest possible audience. Think of a mathematical term that you have never quite understood, click on this link, and all will (probably) be revealed! – An extremely comprehensive set of information on a wide range of mathematical functions, with graphics and many, many formulae. Again, this site is available for anyone to browse.