Picnik is surely the easiest online photo editing site, with amazing UI design and 0 bug ever found in my experience. Picnik basically focuses on adjusting photos into beautiful colors. You can’t do much other work with Picnik, but Ladies will surely like its color.
PhotoFunia is a site just for bloody fun. Upload your picture and choose any effect from hanging yourself on outdoor billboards to putting your head on Superman’s body. Really funny for young girls when you feel bored.
FlauntR is another free site to make your photo fancy, especially adding colorful text & borders to your picture. It’s kind of a static version of Slide.com video effects. I’m not a fan of it, but probably teen girls love it.
Tucia is the largest photo editting site with 2000+ real designers, and human power is the unique feature to make it really stand out. Basically you can ask Tucia’s designer to modify & create anything you want on your photos. The before&after picture at the top of this post is a demo from Tucia.
Fotoflexer is similar to picnik but more complicated designed for pro-level girls. There are some effects which can be only seen in Photoshop.