Icon Machine is a native icon editor for Mac OS X icons, capable of editing in all color sizes and depths. You can draw the icons yourself using the built-in array of standard tools, or import images from an application such as Adobe Photoshop.
Masks are easy - if you paste from an application like Adobe Photoshop, the mask is automatically imported as well. And while you're drawing, the image and mask are automatically kept in sync.
Also included is an "Edit Icon" contextual menu plugin for quickly opening files into Icon Machine from the Finder.
Icon Machine requires Mac OS X 10.2 or later.
Version 3.2 uses modern text drawing and font selection, and fixes various bugs.
You can discuss Icon Machine in this site's forums, see the latest development news, or read the incredible story of how all this happened.