I have uploaded all the skins I can find, along with a screenshot, to the unofficial wiki page -
http://musicbee.pbworks.com/w/page/52878103/SkinsIt should include all the skins from this forum. The skins that are now included with the standard MB installation are listed/screenshot under the Default Skins section of the page.
It would be great if we could keep this up to date and for skin makers to update the wiki when they update a skin or create a new one.
I added them all primarily because I recently went through the forum looking for a skin but the mediafire link was dead, and then I noticed that there are quite a few skins with dead links. It is also easier to scroll through and see which skins you like rather than wading through various topics and questions which may not even have a skin link in them.