Folder Icon Maker

Folder Icon Maker is a Shareware icon utility tool that can be used to combine Mac OS X Finder icons. To use the program, simply drop an icon for the backdrop onto the view in the upper left corner of the window and drop an icon for the foreground onto the view within it. The program will composite the two icons together, with the transparency intact, and allow you to write the resulting composite to a PDF file, TIFF file, .icns file or to the Finder's clipboard.

Limitations:

Nag screen