Sumopaint, by Snap Group Ltd is looking to be a really slick Flash-based online graphics creation and editing tool. It has a very complete list of functionalities with shapes, brushes, layers, text editing, filters, and many of the features you'd expect from Photoshop or (ack) GIMP. Users can share images for community editing, create and view versions, and add comments.
This looks like it might turn out to be an excellent resource for those looking at doing things like shared whiteboarding and prototyping without the real-time editing. On the surface this appears to be only a Photoshop-like tool, but if you were to leverage the community and versioning features, the possibilities for a flexible tool like this become pretty interesting. Check it out.