I came across this site which seems to have lots of good ideas on lots of different topics. Thought I'd pass along the link. Look at this one on productivity. There is a 'top posts' page where you can see lots of her better stuff.
Here is another site that has some great links about brain exercise. See this page on Ten Habits of Highly Effective Brains. The number 9 entry on this last list is to 'develop and maintain stimulating friendships' which I think is one of the most important entries in the list. Connect up with smart, interesting, caring people and spend time with them. This relates to the community posting earlier. More on this later.