DropIt takes some patience to configure, but once you do, it's downright magical. The software revolves around setting intricate rules: for example, you can create a rule that has DropIt sort all the images and music in a given folder into different subfolders, and all music under a certain file size into yet another folder. Then, set the program loose to automagically sort your stuff.
That's all well and good, but I prefer to use DropIt as an awesome tool for keeping my desktop clean. After taking the time to fine-tune a bunch of rules, dump DropIt's small, blue icon in the corner of your desktop.