WindowShade X is another fine little hack from Unsanity that not only restores a feature of OS9, but adds some new stuff too.
The initial controls are simple enough; there is an option to turn WindowShade X on or off, an option for it to play sounds, and a list of programs to exclude. However, it does go much further than simply adding the windowshade option from OS9 to X. You can customize the shadows (shadow spread, shadow density, horizontal offset, and vertical offset) for both active and inactive windows.
With WindowShade X, you can also customize several other functions. You can control what happens when you click the minimize button, double-clicking the window title, control-double clicking the window title, and command-m (if available). There are several different options you can have for these. WindowShade simply folds up the window, just like in OS9. Make Window Transparent is quite cool, as it does just what it says; the entire window becomes transparent, and you can set the opacity. Minimize to Dock does just what the minus (yellow) button does already. Hide Application hides all of the active windows for the program. Then there is the mysterious Do Nothing option; I'll leave that a secret for you to find out when you download the software.
Just like Unsanity's other software, WindowShade X is only $7, or $6 if you order it with one of their other products. WindowShade may not be that important to you as far as productivity goes, but like I said, it's only $6-7.