I recently started posting tutorials I wrote and the templates I use for my plots. Right now, Gnuplot is the only thing here, and with only a few tutorials, but hopefully that will be changing in soon.
I use Gnuplot because it's an excellent, free plotting program that produces professional-looking results suitable for publications or presentations.
As of writing this, I predominantly use Gnuplot version 4.4.3, though 4.6.0 just recently came out and I'll gradually be upgrading to that due to extra features. Moving older scripts from 3.x to 4.x tends to break some things; mostly, the syntax for offsetting labels is now more strict.
Click the plot to see source.