Bill Gates has launched a blog to share his activities and thought with the world. This is quite an interesting read.
You will find topics like "What I'm thinking" which covers his ideas and opinions on things, "What I'm learning" which covers lectures, books and much more, "My travels" to places like Africa and India, and "Conversations" that covers discussions with contemporary problem solvers.
Even though Bill is retired, he seems to be a very busy man. He seems to be involved with all kinds of matters, from world issues like global warming and poverty, the latest technologies, politics and even teaching.
Go take a look at his blog or if you're a Twit, follow him on twitter.