The site which helps me refresh my math related memory from time to time: PlanetMath.org
I can't recall a topic which I couldn't find there, and its database is growing. I personally like it more than Wikipedia.
An interesting Linux distribution (if Linux is interesting at all): Gentoo Linux
It will make you to learn about Linux a bit more than rather more convenient distributions, but not too much, if you don't want it.
A free graphics editor: Paint.NET
It suits all my simple needs, but I think you might like it too. I assume it requires a .NET framework installed on your computer.
A very simple LaTeX editor: WinShell
It doesn't have too much functionality, it is just convenient to run LaTeX on your source. Comparable to TeXShop on Macs. And it's free. Other thoughts: it may also be a good replacement for Notepad.
A more complicated LaTeX editor: TeXnicCenter
It is much like MS-Word or another office application, but dedicated to editing and compiling LaTeX files. It has known issues though.