Magic Folder Icon is a small, free, program from Efreesky, better known for the beefier MagicTweak and Magic Utilities. Magic Folder Icon simply changes the icon of a folder from its default image (a folder), to anything else, provided you've got an icon you like better somewhere on your hard disk. This has a purely aesthetic effect; it's not likely to vastly improve your functionality, but it can make it quicker to spot a particular folder, especially if you normally use a large icon view.
The interface is somewhat confusing, as it's not entirely clear what the proper sequence of events is and the pop-up help is misleading. You select a folder from a typical tree view; then you browse for an icon you like. Magic Folder Icon will show you all of the icons stored within .exe or .dll files, as well as those in .ico files; it can sometimes be interesting to see what icons are contained where. Once you've found an icon you like, you click "Save Settings", and that icon will become the icon of the selected folder. There is also a single button to restore the default system icon for a folder, a nice touch.
Magic Folder Icon is very poorly documented, even given the small set of possible actions you can take. The "Help" file is just a restatement of the product description web page. The "Save Settings" button has a pop-up that reads "Save the autostart settings", which doesn't communicate "Assign selected icon to folder" very well. Last of all, I would expect a program like this to come with a library of sample icons; it doesn't. Fortunately, sample icon libraries are not hard to find.
Magic Folder Icon promises to let you change folder icons, and it meets that promise. Its features are sparse, and somewhat obtuse, but it does the job--and it's free. If you're bored with a wall of manila, it can be worth checking out.