Another generic "intelligence" booster, for certain definitions of intelligence, is learning about cognitive biases and certain reasoning skills - "rationality". When I read the Sequences (http://wiki.lesswrong.com/wiki/Sequences) on Less Wrong (http://lesswrong.com/), I think my reasoning and analysis skills improved, and I was able to avoid some thinking mistakes, such as by training myself to be "fair" to all sides of an argument. I also found reading the Sequences fun; their subjects include interesting mental puzzles. Go check them out.