I donated a computer last summer to the National Cristina Foundation: http://www.cristina.org/
From their website:
"The National Cristina Foundation is a not-for-profit foundation dedicated to the support of training through donated technology. For more than 25 years we have encouraged companies and individuals to donate computers and other technology coming out of their first place of use, which are then matched to charities, schools and public agencies in all 50 states, Canada, and internationally."