From Planeshift Software:
Modify just about any application or file icon using this custom icon utility. Set an icon by cloning the icon of another file or folder. Make your own icons. iThemeOS allows you to create icons from your JPEG, GIF, PNG, or TIFF files. Modify dock icons (Trash, Finder, and Dashboard support provided). Modify the boot panel and login screen background image. Change your storage media icons (hard drives, optical disks). Change a full suite of system folder icons, network icons, and others. Save and re-load your system icon theme packs so you can share them with friends and family.