Picasa was yesterday. Picnik is today. 🙂 Well, seriously, you still need Picasa for working with your photos on the harddisk, but for your online life Picnik is an exciting alternative. An technically impressive flash and ajax conglomerate, really worth to check it out!
PhotoJoJo says (although the comparison to PhotoShop maybe just a bit exaggerated):
Crop, rotate, resize, one-click fix, color adjustments, sharpening, saturation, even histograms. 95% of the stuff you’d do in Photoshop, you can do in Picnik more easily. Grab photos straight from your Flickr (and replace them with edited versions), from your computer, or the web; send your edited photos to your blog, to email, photo sharing sites, make a nifty slideshow, or even have them printed.
Check out Picnik.