Splashup is a free flash based free easy to use, web-based image editor for experienced users, it supports layers and has a interface similar to photoshop.
- Multiple image editing
- Pixel-level control
- Layers of depth
- Brushes & Filters
- Layer effects
- Integration with online image services like flickr
- Fullscreen mode & Resizable windows and panels
UPDATE: Adobe launched PhotoShop Express - An Online image editor.