I'm looking for a free image editor that will do some of the most basic photoshop tasks for OS X Leopard, like crop, brighten/lighten, rotate, and maybe a paintbrush of some sort. I would use it so occasionally, that it's not worth it for me to buy anything serious, or I would (unless someone wants to recommend some $5-$10 app). Are there any thoughts on what's the best free image editing app out there?