Is there a decent icon editor for OS X capable of editing .icns files?

Solution 1:

Is depends on the kind of editing you need to do. icns Editor is on the App Store. Maybe this one too?

Solution 2:

In 10.5+, Apple's built-in Preview.app lets you do edit .icns files!

(Preview used to be pretty bare-bones back in 10.2 days, but with every OS release it has gotten more and more powerful.)

After opening the file, use the up/down arrow keys to switch between the different sized icon and bitmask images contained in the .icns file.

Then with each image you can:

• Cut/Copy/Paste
• Annotate (draw rectangles, add text, lines, arrows, ...)
• Change transparency
• Scale
• Adjust color (saturation, tint, sharpness, etc)