If you are bored by the default Windows 8.1 appearance, try this theme. Base, an awesome work by talented designer 'link6155' is a visual style initially created for Windows 8, but updated few days ago to be compatible with Windows 8.1.
The Base theme provides a black appearance for window frames and the taskbar. It looks suave and attractive. The other good thing about this theme is huge wallpapers pack shipped with the theme.
Size: 51.5 Mb
Download: link6155's deviantart gallery