GIMP 2.8
Posted in Software
GIMP is an open source image editing program. You can use it for a lot of the same things Adobe Photoshop is used for.
They just released version 2.8 (release notes).
In addition to GIMP, be sure to keep up with Inkscape, an open source vector graphics/illustration program. You might be able to do without Adobe Illustrator better than you think.
You can even typeset math equations using TeX. (link)
Both GIMP and Inkscape are available for Windows, Mac OSX, and Linux.