Towel Day
May 25th is Towel Day, celebrated first in 2001, two weeks after Douglas Adams's untimely death at the age of 49. The theme is a celebration of his life and work, with the focus on The Hitchhiker's Guide to the Galaxy. A towel is about the most massively useful thing, and it's celebrated with this theme.
More personally, Clay's brother's last name is Fortytwo. "42" is the answer to life, the universe, and everything. It's too bad that we can never know the question.
This theme was designed with the idea that it would be a single-day theme. It's not quite as complete as some of the later themes.
To install it, please download the self-extracting InstallTowelTheme.exe and follow the directions on the instructions page. (There's also a zipped version - InstallTowelTheme.zip))
Sequoya and Verona have their own version of the install file.
You may also want to check out the Towel Day credits page.