This Vincent Van Gogh doodle, which suggests his Starry Night painting, was featured March 29, 2005, which was his 152nd birthday. This also comes as an art print and a t-shirt.
Google has a number of Earth Day Doodles for different years, including this spectacular design from April 22, 2010. The purpose of Earth Day is to bring awareness to our environment and to the issues that can harm it. All of the Google Doodle Earth Day designs are beautiful.
The DNA doodle is a cool design that shows the DNA double helix. This was featured on April 24, 2003, the 50th anniversary of when James Watson and Francis Crick described the structure of DNA.
January 4, 2006 was Louis Braille's 107th Birthday, and a braille version of the Google logo was featured, as shown on this mug.
The Google musical staff, featured on June 8, 2010, commemorates German composer Robert Schumann's 200th Birthday.
The very colorful t-shirt celebrates Holi Festival, and was featured March 20, 2011. The Holi Festival of Colors is a Hindu spring festival that's celebrated in part by throwing brightly colored powder at each other, and wildly celebrating in general.