I use Gimp with the addin
Gimp Paint Studio which rearranges the window locations as well as adding a number of useful brushes and tool sets. For most uses, I feel like it is just about as functional as Photoshop. I can second Inkscape as a vector editor, I use it all the time. Another good free program is Scribus, which is useful for creating page layouts. I suggest getting the release candidate, as it is much better-featured than the stable version.
-David