Create Icons *.icns for OS X

To create icons for your OS X Applications, first create a master 512pixel x 512pxel master image. create smaller versions if required ie if you want the smaller logos to be different.

The size options you can create for are:
512x512
256x256
128x128
32x32
16x16

Once you have your images, my logo is simple so I only created one 512 master copy, from photoshop save as a tiff with transparency and Image compression:no compression, Layer Compression:discard all layers and save a copy.

Then open (you need the developer tools xcode):
/Developer/Applications/Utilities/Icon Composer.app

Then drag you 512x512 tiff on to the largest square I then let it auto scale this image for the smaller options. Then just go File Save As. and you *.icns file is created.

A very helpful tutorial was.
http://tutorialdog.com/how-to-create-icons-for-mac-os-x/

A generic guide to integrating the icns into your mac app is:
http://stackoverflow.com/questions/646671/how-do-i-set-the-icon-for-my-applications-mac-os-x-app-bundle

Because I am working on a project setup by xCode I can just replace the file in:
ProjectRoot/resources_macosx/projectName.icns