Peter Doyle and Curt McMullen. Web text chatracterising equations that can be solved using iterated rational maps: the Galois group must be within A5 of soluble.
This site has the general algebraic solution to the quartic equation. It also has an example on how to solve the equation that Lodovico Ferrari solved (Ferrari discovered the solution).
Allows the use of many Mathematica functions over finite fields without any modification; e.g solving linear equations, inverses, determinants, derivations, resultants. By Ryoh Fuji-Hara, University of Tsukuba. Package and documentation are available for download.
Methods to solve algebraically several quintic equations. Though quintics cannot generally be solved in terms of finite sums of radicals, they can be solved as infinite series, for example. (Designed as an "on-line poster.")