Pixlr is an advanced free online image editor with powerful features. It also includes one-click effects . There is also an extension for chrome
A fantastic article explaining application of pixlr to improve visual identity.
Other great options:
Photoshop Express is like a light version of Adobe Photoshop that’s both free and requires no installation. You also get 2GB of storage space for saving those editing photographs online
Picnik makes your photos fabulous with easy to use yet powerful editing tools. Tweak to your heart’s content, then get creative with oodles of effects, fonts, shapes, and frames.
Aviary is a suite of powerful creative applications that you can use right in your web browser. Phoenix is their online image editor.