As a successor of Picnik which was my favorite photo editing program at the time, PicMonkey is doing a good job of providing a good number of easy-to-use photo editing tools free of charge. I particularly like the many effects that PicMonkey provides. One word of caution, you can spend a lot of time playing around with your photos, as with most everything else, less may be more! If you haven't used it yet, give PicMonkey a try.