Every modern Mac ships with Apple's developer toolkit, though it's not installed. It's on the DVD. You can also register as a developer (free) and download the latest version (which is what I did today since I'm messing with AppleScript Studio).
Besides a massive (1.3 GB) library of Apple documentation (take that Spotlight!) the Developer install includes several useful tools and at least one semi-frivolous tool: Core Image Fun House. I tried out the perspective manipulation tool. Very impressive.
You can do some valuable image manipulation with this, especially if you don't own Aperture. You can, for example, apply noise reduction, something that's part of Aperture but not part of iPhoto 6. It opened my Canon RAW images (.CR2) without complaint.
It has an interesting export option called "Fun House Preset". This is a package that contains the original RAW file and an plist style XML file.
You can also export as TIFF or JPG. Interesting and potentially useful. I'll test it as an external editor with iPhoto.