Iconographer

Iconographer is a fully-featured icon editor. It allows you to both change the icons of items and to edit the icon resources used by various programs.

Iconographer has been created from the ground up to deal with many icon formats, including: classic Mac OS (8-bit icons only), Mac OS 8.5+ (32-bit icons with 8-bit icons), Mac OS X (128 x 128 icons in .icns files), Windows and Windows XP (.ico files), and Mac OS X Server (48 x 48 icons in .tiff files).