Mac OS X's Aqua UI is a mighty purty thing, what with its oh-so-slightly transparent menus, gun metal finish and lickable blue dialog buttons. But what if you want to mold the look of the Mac OS to your bidding or apply a new theme? We've blogged about the likes of ShapeShifter and CandyBar here at TUAW before, but Appleication just put together a roundup of 10 UI modification apps that can enhance your Mac's look and feel in just about every way possible. Armed with this list, you'll have everything you need to set movies and websites as your desktop background, dim apps in the background to get your concentration on, bring that unified look to all your apps and even add the power of multiple desktops to your workflow. Even better for those of you still trying to recover from the blow to your budget after the holidays, most of the apps on this list are free.