I would recommend Picnik
I do not have a photo editing software in my machine. And needless to say I’m cheap. I do not want to buy any software like Photoshop for simple resizing and sharpening and other basic editing stuff. However I use an online photo editing service by picnik (www.picnik.com), it’s free and I find that it satisfies most of my needs.
Okay if you are like me, probably you need to take a look at this 90+ online photo editing tools and resources (source mashable.com). For the full story click here.
However if you are like me, just looking for basic photo editing tool, I would recommend Picnik.