GIMP is a free (Open Source) program for editing pictures.
GIMP site - The program is available for download here.
Tutorials
| GIMP | ||||
| Carey Bunks | High Dynamic Range photos using GIMP | Katja Socher | ||
| PIXEL2LIFE | GIMP Photo Effects | GIMP Tutorials | ||
| Really Basic Photo Editing |
Another free program: Picasa