Most are lame.
While perusing design blogs, I noticed a couple people's Macs had a sweet vintage flip-clock screensaver. And I figured out how to get it.
Here's what it looks like:
pic via apartmenttherapy
pic via Making It Lovely
It's a free download. You can get it here. (Pssst....it's the one on the left!)
And to my non-converted friends.... it's available for Windows too. : )