My desktop has 3 monitors with lots and lots of windows. On Windows 8, it gets really fatiguing picking out the active window. That’s because Windows 8, unlike Windows 7, doesn’t have shadows. It’s one of my biggest pet peeves with Windows 8 visually.
This wasn’t a problem with Windows 7 because each window had its own drop shadow which changed based on what was the active window. As a result, at a glance, you could pick out the active window.
To address this, Stardock, the makers of Start8, Fences, ObjectDock, Launch8, ModernMix, etc. has released ShadowsFX, a simple little program that simply adds shadows back.
Users can pick from a series of shadows. I find that a medium shadow works the best but your mileage may vary.

Stardock ShadowFX in action
To Download:
https://www.stardock.com/products/shadowfx