I just discovered this great website called Free Rice. Set up by the people at poverty.com the site has the twin aims of offering a free way to enrich English vocabulary and helping end world hunger by providing free rice to the hungry.
The site works by a simple process of matching words to their meanings; each correct answer earns a donation of 20 grains of rice to the World Health Organization. There is a feature to hear the word and the site remembers your vocabulary level and total donations. Funded by non-obtrusive advertising at the bottom of the screen it really is a fun, easy and slightly addictive way to make a small difference. Checkout the website.