Adobe Photoshop seems to be the standard that all the graphics professionals use for their image and graphics creation and editing needs. Certainly Gimp and PS Elements will handle .psd files, but they don't offer the advanced features that really set Photoshop apart.
Right now, you can get your own copy of Photoshop CS2 for Windows or MAC at zero cost. Granted, this is not the latest version of PS (CS6) and I think Adobe is moving toward their cloud based model where you pay a monthly fee to access their software.
But CS2 is still Photoshop and it is very powerful (and there is no monthly fee to pay with your own software program). Here is the download link:
Adobe Photoshop CS2
Take notice of the Windows or MAC serial numbers you'll need below the download button. Copy them for later use in running the software.
You might be concerned about the PS learning curve. There is one, but there are also tons of "how to" resources online that will walk you through most Photoshop (PS) functions. YouTube has thousands of video tutorials on PS.
Here are some good free PS CS2 tutorials on Vimeo:
35 more free Photoshop tutorials:
More CS2 Tutorials
If you've ever wanted Photoshop but couldn't afford to purchase it, now is the time. Take action and stay thirsty my friends.