Paint.NET
I started using this software a couple of years ago when I was trying to create a logo for my first blog. Paint.NET looks simple but actually loaded with lots of features found in Photoshop. It’s an open source software with many plugins that can improve it’s functionality. As a matter of fact, you can even edit a .psd file with this software, re-touch your photos and do much more. It’s a pretty good alternative to Adobe Photoshop for a casual graphic artist / logo designer.
Pixlr Editor
I started using this on my iPhone and if all you care about is a nice looking picture with some professional looking touches you can easily apply, you’re gonna love the web based version of this app. Of course, it’s free but it’s a web based app that should come in handy when you’re thinking of re-touching your pictures on Facebook, Google+ and other social networks
Adobe Photoshop Express
Just like Pixlr Editor, Adobe Photoshop Express is another free web based tool that lets edit your pictures online without the need to download any software.
GimpShop
If you’ve used GIMP, you’ll definitely love GimpsShop as it is built based on Gimp but with the classy look and feel of Adobe Photoshop. It’s a great alternative to Adobe Photoshop.
PhotoFiltre
PhotoFiltre allows you to edit your photos easily and add filters to make them look better without knowing much about graphic editing. It’s quite easy to use and the user interface is easy to understand.
PhotoPlus
Editing your photos is made easy with PhotoPlus (starter edition). If all you want it just to adjust contrast and brightness, whiten teeth, make your skin smooth, remove certain objects from pictures and apply certain effects to your photos, PhotoPlus is just waht you need.