You can donate to some good causes simply by buying products through Amazon associate links.
Even if you're not interested in making money by linking to Amazon, there are some organizations that could use the help. Though revenue from affiliate fees for an individual site is small, many small contributors working together can generate contributions that add up.
GiveQuick (http://givequick.org/) is an organization devoted to aggregating affiliate fees for nonprofit organizations. They have a list of their organizations on their site (http://givequick.org/core/directory.php3).
With a special linking format called Giving Tree, you can link to Amazon products through the GiveQuick site, and they'll distribute any affiliate sales to their organizations. Setting up a giving tree link is similar to setting up an Amazon associate link [Hack #59]. Just add the ASIN of the product to a GiveQuick URL:
This URL will redirect to the proper Amazon detail page, and one of the member charities will receive any affiliate fees. If you're linking to Amazon on your site anyway, it's an effortless way to help out some worthy causes.