Are you fed up with those boring 'embossed' blue folders for Documents, Music, Pictures etc? No problem -- just make your own!
Navigate to /System » Library » CoreServices, and view the contents of the CoreTypes.bundle bundle (Control-click and select Show Package Contents). I recommend copying the Generic Folder icon file to your desktop for easy management, but if you look at the other .icns files in there, there's a whole host of goodies!
One thing I've done is copy an image on top of the generic folder using Preview. Just select the image and use copy/paste to paste it onto your generic folder. Because these icons are 512x512 and properly masked, you get a nice overlay with transparency, too (for some, at least). You can move also move the pasted image around like a layer in Photoshop.
Once the image has been modified to your liking, click on the image again in Preview -- this will flatten it. Then use copy and paste to change the icon in the Get Info window of your boring blue folder ... straight from Preview; no other software needed.
One nice example is having a folder with the green "downloads" icon on it that you see in the sidebar -- good for easily recognizable stacks. Have fun!
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080220080521648