I know not all of us can afford to purchase or have access to copies of expensive software like Photoshop or Illustrator, but there are other alternatives out there and they are free!

(1) GIMP: GNU Image Manipulation Program - This is my favorite, it is a wonderful image editor and it works wonderfully as a replacement for photoshop. You can even vector in this.

(2) Terragen - This is an extremely awesome landscape generating program. It is very powerful, and creates detailed work.

(3) Pixia - Cant afford painter? Well this little software piece comes close to the quality of painter graphics. Its very intuitive design and can be used to prepare fairly nice painted anything.

(4) Apophysis - A fairly complex fractal generator. Good for creating abstract effects. Beware of long render times.
(5) POVRay - A ray-tracing program that you can use to generate 3D images. Not very intuitive and unless you're comfortable with the interface, difficult to generate anything beyond basic polygon-type imagery, and slow render times, but it can be useful for abstracts.

(6) Paint .Net Paint.NET is image and photo manipulation software designed to be used on computers that run Windows 2000, XP, Vista, or Server 2003. It supports layers, unlimited undo, special effects, and a wide variety of useful and powerful tools.

(7) Inkscape Inkscape is a vector program, much like Illustrator, with some tid bits of Flash, and is fairly nice to use. I tend to use it with my tablet due to the free draw option, but it does have the workable paths/anchor option if you don't want to try and free hand it. Works on Mac OX, Windows, and variations of Unix/Linux.