In addition to iGoogle Themes released in November this year, there's an additional iGoogle theme called Winter Scape. It was available back in March, when Google launched themes, but it was replaced by a theme for spring, now known as Seasonal Scape.
Description: "Brrrrr! Wintertime is here and there's snow on the ground. This friendly snowman will keep you company on your iGoogle homepage as the day goes by."
go to iGoogle, paste the code in the address bar, press Enter and click on the Save button in "Select a theme for this tab" to keep the new theme.
The PI easter egg in the second screenshot above is powered by Tony Ruscoe's JS tricks.Google, iGoogle, Theme, iGoogle Theme, Google Personalized Homepage