Honestly, I don't use screen savers that much anymore - however, I might fall back into the trend, due to this awesome free one I found the other day.  It is called, Briblo.  You can kind of think of it as a mix between Tetris and playing with your Lego bricks.  Tons of fun!

Also, on that same site, they have Fliqlo, which will display a large flip-style clock as your screen saver. 

See, two for one deal here!

http://www.9031.com/downloads/screensavers.html

Yep, I'm still using it - sure beats some of the Windows default ones.