I just stumbled upon a cool website called Free Rice. It's an interactive vocabulary builder. For every word you get right, they donate 20 grains of rice through the UN to help end world hunger. Check it out @ http://freerice.com!
I blogged about this a few weeks ago, and I found another site where you can just click to donate food thanks to the site's sponsors. Not as cool as improving your vocabulary, but along the same lines and being helpful to the needy :)