Found this list at mashable.com, all free software.
Paint, Drawing and Graphics Programs
Gimp – Very powerful image manipulation program, great for photo retouching and image creation. There are other downloads, GTK and runtime environment for this program to work properly. This program currently runs on Linux, Windows (XP and Vista), Mac OSX, and some Unix based systems.
Ultimate Paint – Image creation and manipulation program for Windows systems. This is a pretty compact and fast running graphics program with plenty of features.
Skencil – An interactive vector drawing program for Unix and Linux operating systems built on the Python language. This program has tons of features like gradient fills, bezier curves and you can bend text along paths to name a few.
Pixia - Originally a Japanese only edition, Pixia is a very nice paint tool with full layers support and many other features. The English version website does lack information and support so you will likely need to search the web for information on learning to use this tool. This is currently a Windows only program and does support some drawing tablets.
InkScape – If you have been looking the free answer to Adobe Illustrator or CorelDraw, IncScape is a great alternative. This is a full featured vector graphics editor. The website has a tons of information, tutorials and galleries of work created with the program, to give you a good idea of what you are getting involved with.
Paint.net – A free image and photo editing software for Windows based PC's. This program was voted #19 out of the top 100 programs of 2007 by PC World. It has full support for layers and special effects, the tools are top notch and highly recommended by many users. There is a strong online community for support and frequent updates to the software. Comparable to Adobe Photoshop.
SmoothDraw NX – A freehand drawing tool designed for use with tablets. Several choices of brushes and pencil strokes for creating realistic drawings. Also auto smoothes lines if you are using a mouse to draw with.
ImageForge – An image editing and creation program for Windows systems. Although this program is a little rougher than some of the others it still has some nice features like easily creating 3D text, red-eye removal and you can easily create your own Windows screen savers.
Brush Strokes – Free graphics editor, with support for many of the popular and common image formats. It isn't as full featured as some of the other programs but it is a good choice for less technical or light users.
Project Dogwaffle – A painting and drawing program developed for the PC. Has a nice set of tools and very functional, although does lack features of some large programs.
Sodipodi – This is a vector based drawing program that operates on most Unix and Windows systems. It has a ton of features like out of center gradients, patterned lines, dynamic xml editor and you can easily create vertical text.
Karbon14 – Another nice, full featured vector based drawing program released under the GNU license. This program comes as part of the Koffice project which includes a whole suite of tools in KDE.
ArtWeaver – A freeware paint and drawing program for Windows designed to simulate natural brush tools and effects for artists used to working on canvas. It supports most common file formats, has the standard editing tools like found in many popular graphics programs and offers a few effects filters.
GimpShopdotnet – This is a modified version of Gimp, designed to work and feel more like Adobe Photoshop, allowing Photoshop users a comfortable free alternative.
ImageMagick – A nice command line program for editing and creating images. There are a whole bunch of useful features like shearing and transforming images, flip, mirror and rotate images and a whole lot more.
Animation & 3D
Terragen – Create amazing scenery and photorealistic images with this program. This program comes with a lot of features including, terrain sculpting tools, water and cloud generators, realistic sunlight creation and so much more. Works with Windows and Mac OS systems.
Google SketchUp – A powerful 3D software that allows quickly build 3D models. The program is pretty easy to use and you can design and build everything from your dream house to a favorite skyscraper. Works on Windows and Mac systems.
Art of Illusion – An open-source 3D modeling and rendering studio written in Java and usable on most Java Virtual Machines. On the website you can find some comprehensive tutorials on creating a human figure, working with triangle meshes and more to give you a little better understanding of how to use this nice program.
Blender – A top of the line 3D graphics program available for most operating systems. This is a very powerful tool but does have a strong learning curve if you are not familiar with these types of programs. On the website you can find a bunch of great tutorials, galleries of previous work created with this application and a busy community to answer any questions you may have.
3D Canvas – A real-time 3D modeling and animation tool. Easily create 3D scenes with drag-and-drop controls. Customizable toolbars and interface and frame by frame animations are only the start of this programs features.
Graphix – An open source graphics editor built to edit and create both raster and vector images. Works one WINE and WinXP operating systems.
3D Plus – This program definitely lacks some of the features of other full scale 3D programs, but it is very ease to use and works well for small quick jobs. You can also purchase the extended version for $9.99.
Daz 3D – Calls itself a figure posing and animation tool, basically you can use pre-created people, animals, vehicles, scenes and more, to edit and manipulate them to create your own 3D and animated scenes. The program itself is free, however most of the additional add-ons will cost you money. With that said this is a very nice program to use for people of all skill levels and highly recommended by many.
Anim8or – A 3D modeling and animation program, that is available for download, but kind of a still in progress program. It does have its bugs but is a very nice program created by one person to handle what they wanted out of 3D software. Some of its features include, a built in 3D object browser, true-type font support, 3D modeler, jointed character editor and a bunch others.
Synfig – A very powerful, well developed 2D vector animation program. This program was designed for studio quality animations, why it was released under the GNU license for free, I have no idea, but I am glad it was. It is currently available for Windows, Mac and Linux operating systems.
BRL-CAD – A cross platform 3D modeling program that includes ray-tracing for rendering, interactive geometry editor and more. This program is not recommended for non-tech users.
MindsEye – A nice freeware 3D modeling and rendering suite for Linux users. Features include a multi-scene/user concept that allows multiple people to work on the same scenes or visa-versa, object oriented modeling, network support in the MindsEye kernal and more.
Maya Personal Learning Edition – Maya is an excellent, although expensive 3D graphics program. This is the free edition developed to give you the opportunity to learn and use the program before purchasing. This edition has most every feature available as in the standard version but it is for non-commercial use and your images will be watermarked among other things.
http://mashable.com/2007/10/27/graphics-toolbox/