So Adobe has released their web based photoshop. Its not a full photoshop (unsurprisingly) but it is free and available anywhere you have a browser.
I tried it out – First I was annoyed by the “US only” thing at registration, so I said I was in the US. then I was frustrated by how long the flash login box took to load up and then I found that I cannot import a single photo as it thinks they are all corrupted… I suspect it is because I am running Linux.
There is a brief review on Photojojo too, though they seemed to like it.
If you are looking for an online photo editor, its worth trying picnik too