Thumba - A Fully Featured Free Online Photo Editor
Sure, most of the time you don't need an online photo editor. You've likely got at least one good image editing program installed on your computer, and it's a lot more robust than Thumba. But if you're on a netbook, at a friend's house, or on a public computer that you can't install programs on, web based image editing may be your only option.
Thumba is a program based on Silverlight that's a lot more robust than most web based image editors. It handles the basic functions like cropping, resizing and the like, but it does a lot more too. You can auto-correct the brightness, contrast and color balance of your image. You can even create effects, add and remove noise, and add lens flare.
If you really like Thumba, you can even download it for offline use. The program is free to use both online and off. Just point your browser over to Thumba.net and get editing.