Ellyssa Kroski from the iLibrarian ( one blog I highly recommend) listed "10 Free Web-based Alternatives to Photoshop".
Library Blog Buzz has covered a few of them: Picnik, Photoshop Express, but if you have to resize, edit or optimize a few pictures everyday, it is worth looking up the other alternatives: Splashup, Phoenix ; Snipshot; flauntR; Pic Resize; Pixenate; Foto Flexer and Phixr.
Maybe, you will find a time saver and a favorite. Web, photo and content editing systems are becoming more and more open to the public, since we are now living in a shareable Web 2.0 world.
Library Blogs Buzz 