I like how working on web performance is so well aligned with other worthy goals. A fast site is site more accessible to other people. A fast site tends to convert better. Using web standards and more native web technologies tends to lead to a faster site.
SpeedCurve has published a pretty beefy and useful guide to Web Performance, and Google’s guide is also good. Of course, our Web Performance Fundamentals course is best for a guided walkthrough of all the most important aspects.