Each November, men grow beards to celebrate beardvember. This started out as an internet joke, but rapidly evolved into a campaign for raising cancer awareness, and a fundraiser for cancer research.
No president has worn a beard in office since Harry Truman's goatee on a brief vacation in 1948, and no president since Benjamin Harrison has worn a beard for any sustained amount of time.
President Obama could lend a lot of support to this simple, slightly silly, yet noble cause simply by doing nothing more than neglecting to shave this coming November.
(P.S: Please let him do it, Michelle!)