Babygimp is an icon editor for Linux written in Perl/Tk. The goal of Babygimp was to provide an icon editor which is easy to use and easy to install but nevertheless provides enough features to create really cool icons.
GNOME Iconset Builder
GIB (GNOME Iconset Builder) allows you to create icon themes for GNOME with ease. No more manual copy/resize/move/convert/rename actions.
The icotool program converts icon and cursor files into a set of PNG images. (Each icon/cursor file may contain multiple images, usually of different sizes and with different number of colors.) Icotool can also create icon/cursor files from PNG images.
png2ico converts PNG files to Windows icon resource files. If you're looking for a program to create a favicon.ico for your website, look no further.
SVG Icons project has a goal to provide Open-Source reference implementation of SVG icon themes for leading Linux and UNIX Desktop Environments, in particular (but not limited to) KDE3 and GNOME2 Desktop environments.
Tile Driller is a simple paint program for people, who want to draw tile based graphics pixel by pixel. It features easy editing of alpha channel, reads BMP, JPG, PCX, PNG and TGA images, and writes 32bit RGBA PNG images.