I've noticed a few people using this online editing site but not posting the link to it, which I feel is unfair.
It's pretty good. You can add text and pictures and all, as well as editing transparency of the both. You can edit colour, contrast, add tints and heaps of stuff.
You can even upload pictures from your MySpace, FaceBook, etc.
You can pay for extra editing things, but you shouldn't need them, it's a good site without having to pay.