Here's some useful online apps...

10 Free Web-based Alternatives to Photoshop
LifeClever has put together a nice list of 10 free Web-based applications which can be used for photo-editing. Be sure and check out the full post for screenshots of each:

• Picnik
• Splashup
• Phoenix
• Photoshop Express
• Snipshot
• flauntR
• Pic Resize
• Pixenate
• FotoFlexer
• Phixr

These were posted to iLibrarian (which posted them from somewhere else).