picnik
crop, rotate, fix colors and exposure, remove red eye and edit photos in other ways... plus fun effects and unique displays for your photos
http://www.picnik.com

Big Huge Labs
fun effects and unique displays for your photos
http://bighugelabs.com/flickr/

dumpr
fun effects and unique displays for your photos
http://www.dumpr.net

Pixlr
sophisticated photo and image editor (includes layering)
use Pixlr Express version for quick editing (cropping, rotating, effects)
http://www.pixlr.com

Sumo Paint
sophisticated photo and image editor (includes layering)
http://www.sumopaint.com