LaTeX is a document markup language and document preparation system for the TeX typesetting program. The term LaTeX refers only to the language in which documents are written, not to the editor used to write those documents. LaTeX is most widely used by mathematicians, scientists, engineers, philosophers, lawyers, linguists, economists, researchers, and other scholars in academia. LaTeX is intended to provide a high-level language that accesses the power of TeX. LaTeX essentially comprises a collection of TeX macros and a program to process LaTeX documents. Because the TeX formatting commands are very low-level, it is usually much simpler for end-users to use LaTeX. LaTeX was originally written in the early 1980s by Leslie Lamport at SRI International. It has become the dominant method for using TeX. As it is distributed under the terms of the LaTeX Project Public License (LPPL), LaTeX is free software. See: http://en.wikipedia.org/wiki/LaTeX
OK, enough quoting from Wikipedia. Back at my time at university I preferrred LaTeX and the beamer package for creating presentations and posters. My collected knowledge on this can be found here.
A quick & dirty guide to a custom (color)theme
Creating posters e.g. for conferences using LaTeX. A short overview of options.