There is a Custom Icon thread over in the Monkey Island forum, and after much fiddling with making MI icons, I also started making icons for my game folders, and it was then that I thought that there should be a thread for custom made icons (ie. icons used to replace the default icon for a program) here in the General Chat forum.
First, if anyone cares, here is a template that was used to aid in making many a fan-made Monkey Island icon.
Second, if you are going to/wondering how to make a custom icon easily, a method that I have found highly effective is to use an image (preferably .png) that is 256x256 in dimension, and upload it to http://www.iconverticons.com which will convert the image into an icon file which contains every available size.
(it can also convert icon files back to normal images as well)