In the case of Facebook, there are several of them, but I have selected five that are adapted to the new version of Facebook and are as follows:
Vista Ultimate Skin for Facebook: I've seen that in this article and give a stylish appearance to Windows Vista. The bottom bar is an imitation of the Windows taskbar:
Facebook Dark Shiny Blue, transparency: if you're bored with the look and like the blue, try this (there is a style like this for Gmail, the same author):
Facebook 2009 Green color: green background, with slides:
Facebook love & Pink Skin: Similar to above, in shades of pink and transparencies:
Facebook Spring Skin: Spring on the occasion:
To use these styles need to have installed the extension Stylish, you can install on this link.
Although I like the dark skin I have not seen any that work well with the new version of Facebook.The great thing about this is that it is not difficult to create styles based on code from another.Even create them from scratch is not difficult to learn but rather by modifying other stylesheets.Just need to know something basic CSS and the rest is imagination.