Ensemble Methods
Boosting
AdaBoost
Robert Schapire did his Phd thesis on boosting. Since then he has done many development in the boosting. He gave a nice introduction to the depth of boosting in the machine learning summer school
In depth tutorial of Adaboost by Robert Schapire
He also has the book Boosting: Boosting Foundation and Algorithms
Boosting can be view as the zero sum game playing using minmax
Gradient Boost
There has been cases where the overfitting will be problem in the adaboost. so the solution is to move in the direction of function gradient. This idea is illustrated in
Gradient Boosting by Mason etal
a tutorial on gradient boosting by Friedman