Here is a free dishcloth pattern that utilizes the Pink Breast Cancer Ribbon: http://www.knittingknonsense.com/pinkribboncloth.html
Black is one that I look for as I lost a brother to Melanoma. I have a son in the US Army, so yellow is another. Here is a list of all of the commonly recognized ribbon colors and their meanings:
Dishcloths are so easy and quick to knit that you could knit up a whole plethora of them, for every cause imaginable.