gimp
How to create a favicon.ico with GIMP
UPDATE: Theres an easier way to do this here: http://www.htmlcenter.com/blog/creating-a-favicon-for-your-website/. http://linuxproblem.org/art_19.html By Mathias Kettner : You need an image file that GIMP can open (PNG, GIF, etc.). And you need the command line tool ppmtowinicon from the netpbm-tools (on SuSE you