"Chandra Wilson, star of ABC's Grey's Anatomy and Tim Daly, star of
ABC's Private Practice, have been named the 2008 ambassadors for Lee
National Denim Day -- one of the country's largest single-day
fundraisers for breast cancer, benefiting the Women's Cancer Programs
of the Entertainment Industry Foundation."

Source:
http://www.emediawire.com/releases/denimday/2008/prweb993434.htm

Also two videos on youtube about the cause:

http://www.youtube.com/watch?v=gDLMuwMpQVo

http://www.youtube.com/watch?v=qcYcMI6CrN0