A good simple howto on writing letters and envelopes using LaTeX. http://en.wikibooks.org/wiki/LaTeX/Letters
LaTeX
LaTeX Coolness
Sorry if this is nerdy but, I love LaTeX... Professional quality beautiful typesetting. You can create attractive documents with just an installation of tex-live and a text editor. You also need to install the tex-live extra's sudo apt-get install texlive-latex-extra...