Pixelmator, the beautifully designed, easy-to-use, fast and powerful image editor for Mac OS X has everything you need to create, edit and enhance your images.
Now it’s available public release you can get it from http://www.pixelmator.com/.
It have many good features and can be used for image editing other than Adobe Photoshop. i use it since adobe is kinda heavy on my imac.
Price is $59.