I (slightly) modified the right hand side of my blog to include some charities that I support. In some cases, I have good friends that have dedicated their professional lives to helping to build these organizations.
These don't even begin to scratch the surface of great organizations that offer great ways to help others. I listed these because I know a bit more about them personally and I'm confident that they do good (efficiently!). Another good friend, Edwin, recently added a blog post on Abilities United, which works with kids experiencing challenges in development and gives them special attention based on their needs. Take a careful look at Abilities United: they deserve support and all the help they can get.