Mashable today posted about 20 Great Online Image Editors.
Many of the sites they wrote about can be found on my website under Photo-Editing (you’ll also find many more there). The Mashable post, though, has some nice screenshots and descriptions.
For my purposes, and for the purposes of my students, I don’t think there’s really much difference between any of them. You can learn more about the online photo-editing applications I’ve written about here.
You might also be interested in The Best Online Sources For Images.