Adobe Photoshop is pretty much the standard program everyone use to edit images. It is a great piece of software, but unlucky, incredibly expensive. It has a lot of features, but sometimes, I just want to quickly crop an image or change its contrast and it is annoying to wait ages for it to load. Anyway, while searching for a way to allow users of my German Anime community (animechat.de) to edit their avatars online, I stumpled upon pixlr.
WOW! I never knew that it is possible to edit images that comfortable in my browser. The best thing is that it starts instantly. No need to wait at all, I can just open it up and use it. Perfect. If only Photoshop could be like this… Anyway, pixlr supports a lot of features, not only the basic ones like Painting and Cropping/Resampling. You can use Layers and apply quite a lot filters to your image. I strongly suggest you giving it a try.
It also offers an API to integrate their image editor to your page for editing Images on your website. I am using it on my community now. You can see some more screenshots of pixlr on the tutorials on the community site.