There are lots of online image editors, Adobe have a photoshop inspired one (http://www.photoshop.com/tools?wf=editor), there's Aviary, Sumopaint, Pixlr, ... I looked at a few a while back http://alicious.com/online-image-editing-update/ and settled on Pixlr.

Try http://pixlr.com - they got both express version for simple tasks, and full photo editor with rich features. For my needs it's better as PS - load faster, dont crash, and I can work with it everywhere.

I would recommend http://pixlr.com/editor/ as a web based alternative.

(Disclaimer, I work for Autodesk but not on that product)

What for you need it?