Useful graphical tools

[Wohlstand]

ImageMagick
Command line batch image converter.
ImageMagick page: http://www.imagemagick.org/
Windows binaries: http://www.imagemagick.org/script/binary-releases.php#windows
Warning, Don't forget to include it into the PATH value!

GIMP
Cross-platform professional raster graphics editor
Gimp page: http://www.gimp.org/
Windows installer http://download.gimp.org/pub/gimp/v2.8/windows/gimp-2.8.10-setup.exe

Inkscape
Cross-platform professional vector graphics editor
Inkscape page: http://www.inkscape.org/
Windows x86 installer: http://downloads.sourceforge.net/inkscape/inkscape-0.48.4-1-win32.exe
Windows x64 installer: http://www.partha.com/downloads/Inkscape-0.48.4-64bit.exe

[Veudekato]

Paint.net
Free and easy paint for beginners and pro
Paint.NET Home: http://www.getpaint.net/
Tutorials: http://forums.getpaint.net/index.php?/forum/18-tutorials-publishing-only/
Download: http://www.getpaint.net/download.html

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Pinta
This OpenSource-variations on a theme Paint.NET. Suitable for users, and Linux, and a Mac, and Windows.
Official site: http://pinta-project.com/
Download: http://pinta-project.com/

[Veudekato]

Krita
One of the finalists Packt Open Source Awards 2011, along with Blender and GIMP.This is another KDE editor to create sketches and drawings, as well as for handling graphics. Mainstream - illustration, concept art and other creative.
Official site: https://krita.org/
Download: https://krita.org/download
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Irfan View
One of the most popular tools for viewing images on Windows-based systems. Smart, compact, free. Is able to open every possible graphics, convert it to the desired format, optimize, create slideshows. There are plugins, skins and localization. Often in opposition to ACDSee.

Site and download: http://www.irfanview.com/