Here is a short list of amazing screensavers that you can download for free.  Check them out! 

Pixelbreaker:

This is version number 3 and it just keeps getting better and better. Windows & MAC.

Link

Electric Sheep:

Now this is one cool screensaver. It is actually open source and thousands of people have contributed to it. How do they contribute? Well, when their computers “sleep”, the screen saver comes on and the computers communicate with each other by the internet to share the work of creating morphing abstract animations known as “sheep”. Its fantastic. Windows, MAC & Linux.

Link

System47(StarTrek):

This one is for all the nerds who love Star Trek. Personally, Im a Star Wars fan, but I do like this screensaver. It turns your desktop into the library system from Star Trek. It will runs scans of the universe and the Enterprise. Windows & MAC.

Link