Everyone knows about GIMP, the open source graphics editor that competes with Photoshop for editing bitmap images, or images with "pixels in a bitmap." But what if you need a free program that can work with vector-based images, such as those that Adobe Illustrator builds? Inkscape is an open source vector graphics editor that runs in the X11 environment compatible with Windows, Linux, and Mac OS X.
Inkscape can import many and work with many of the common graphics formats, such as JPEG, PNG and TIFF, and can export as PNG and many of the common vector-based graphics formats.
GIMP and Inkscape combined can offer many of the same capabilities of their much more expensive cousins Adobe Photoshop and Illustrator. If you're looking to build a graphic design machine on the cheap, you should at least check out these open source programs. They may just suit your needs.