iGoogle Theme Directory:

iGoogle will soon let you create your own theme and upload it to a directory. The documentation for building themes is very detailed and you can already select some themes created by famous designers: Troy Lee's Supermoto Mayhem, Yves Behar's Earth-light, John Maeda's Simplicity is Complex, Mark Frauenfelder's Adventure in Lollipopland and a new theme created by Google: Countryside.

"The Themes API lets you create custom designs for iGoogle. Themes are visual designs that personalize iGoogle pages for millions of users. Themes are not just static designs--they can change throughout the day to reveal a visual storyline, message, or anything else."

Google Code Blog encourages everyone to personalize iGoogle. "Creating your own theme isn't rocket science. If you can create a webpage, then you can create a theme. There are only three steps involved: designing images for the header and footer, entering metadata and color information in an XML file, and submitting the theme."

Update:

More themes (not yet included in the directory): Projected Box (3-D rendering of colorful projected boxes), Books, The Sims 2, Spore, Eat Every Sandwich, Harvest Party, Chris Anderson's The Long Tail.