I used to use Picnik for editing some of my photos - loved that it co-ordinated with Picasa. Picasa now has many of the Picnik features added into it but I have been exploring a few of the other editing options online...
www.ipiccy.com - looks a lot like Picnik
www.picmonkey.com - created by two of the former Picnik designers, they think it's even better
- I got this info from Interface Magazine, Term 2 May 2012 issue, page 47 - Article by Greg Adams.