Online image editor are build with Ajax, Javascript or Flex. Some of currently free online image editors are below
Splashup - http://www.splashup.com/
Splashup is build in Adobe Flex. It look like Photoshop and menu are similar to Photoshop. You can edit online shared album files also [like picasa,flickr etc]
Picnik - http://www.picnik.com/
It as additional Firefox plugin api for faster access
Adobe Photoshop Express - https://www.photoshop.com/express/landing.html
You have option to store 2GB of photo and use Adobe to edit photos
