Things to Prettify Your Mac

Breve Creatures screensaver the breve simulation environment.

IdleWeb view and scroll through websites as a screensaver

LotsaSnow - Pretty snowflakes fall against a background or over your dimmed desktop. I love this.

FuzzyClock tells the time in an around and about way.

and many localizations including Pimp-not sure wether this will be a permanent feature in my menu bar.

vUpstream is fast and flashy, but quite nice.

Oh and

ShadowKiller removes window shadows and speeds up my aging iMac (G4 800mhz). Not a prettyfier, but it does change the GUI.