Google, Microsoft, AskJeeves and Yahoo! are supporting through their technology recently launched Goodtree.com a search engine that at each query donates profits to a charitable cause a user chooses (environment, health, poverty, etc...). The site also enables to invite friends and keep track of growing network of users (aka charity tree) and homepage customization. Charities are selected by independent third-party groups (their about page) and users can select the benificiaries of their searching.
A brilliant example of social enterprise.

Waterborne illness kills 6000 people a day. LifeStraw kills 99.9% of disease causing mico-oragnisms in drinking water. It costs less than a happy meal (source Wired Magazine.