Photoshop and Gimp are much more complete, but if you're not a professional photographer, Pixlr should more than fulfill your needs. Best of all, you don't have to install, download anything. It's in the "cloud." A little bit like Picmonkey, but much more complete.
It's three flavors are:
Editor(advanced), Expressed(efficient), Pixlr-o-Matic(playful).
