Pixlr is a new web-based image editor. Its interface is pretty simple, and the loading speed is very fast. There are some other similar services which i introduce before, such as Sumo Paint, Photoshop Express, Splashup, and Picnik.
There are a lot of tools which you can use. For example, they provide marquee tool, stamp tool, blur tool, filter, and even add new layer to the image!
The entire application is based on flash and contains almost all features of a basic image editing sotfware. You may give it a try if you want a simple yet fast web based image editing tool.