Well, in addition to GIMP, I've got Inkscape which is a drawing programme. I plan to get a graphics tablet for that one (recommended) and I also have Celtx for scriptwriting. I use Open Office for writing, and just downloaded a desktop publisher.
I also did a caricature of Londo Mollari (Babylon 5) which I posted on my Facebook page, as I assume non-trek characters are verboten on this forum.