TeX and LaTeX

TeX Live:
The recommended TeX installation is TeX Live.
The recommended integrated writing environment / text editor is TeXstudio.

Links that might be of some interest:

Single packages can be downloaded from the CTAN archive.
The TeX Catalogue Online can be useful when searching for a package that solves a given problem.
IMFUFA LaTeX
W32TeX – the Win32-implementation of TeX Live.

User groups:
There are TeX user groups all over the world. Here are two of them:

Demos, summaries and guides: