For the honest people out there who don't want to use pirated software and are looking for a great image editor without costing too much I recommend having a go at Pixelmator.

It just got a major update today and it's available through Mac Appstore for aprox $30, and for those of you with Pixelmator 1.x.x already installed the 2.0 update is free.

And no, I'm not affiliated with them in anyway. I just like the software and it only cost a fraction of it's competitor(s)

I find that Gimp does everything I need. Free and available on many platforms.