Latex

Latex is an incredible tool for creating beautiful documents. Here's how you can get started with Latex in Ubuntu:

Install latex (texlive is a Latex distribution):
sudo apt-get install texlive-full -y

The Kile Latex editor is pretty nice (it relies on kpdf and kdvi for document viewing):
sudo apt-get install kile kpdf kdvi -y
kile

Inside Kile:
New -> Article -> Ok

And you're off! There are plenty of Latex examples on the web

Links:
Visual Latex Math Formula Documentation
Latex Documentation
Latex Graphics
Latex Tables
Latex Trees