Gimp Image Manipulation Tool
Get the GIMP, you simply won't regret it. It may be a little awkward to use at first but once you have been able to master the GIMP it will serve you well.
Gimp is used by many a freelancer or hobbyist and is a great alternative to using Photoshop, especially because of the price. GIMP is free to download and use forever. You can, however, offer a donation to help keep the project updated and supported.