Pheonix, by Aviary, is wonderful and fairly easy to use if you consider how robust it is. You can manipulate images without downloading software, save the images (on Aviary's site with a free account), and download the images. You do not need to sign up or sign in to download your creations. The account is just for saving to edit later on.
Pheonix seems as capable and robust as Photoshop, but is a lot easier to use. It automatically generates layers of your edits so that you can manipulate aspects of the image separately.
Being browser-based, all you need is a decent Internet connection and you can work on your photos and images from anywhere.
Don't miss the cool video on the opening page that fast-forwards through a project flow in creating the above image.
Pheonix can be found here: http://aviary.com/tools/image-editor
There are over 70 tutorials here: http://aviary.com/tutorials?tool=Phoenix