Practical and powerful article from Edutopia on project-based learning: New Skills For A New Century. They've also got a whole content section devoted to the topic.
On a related note, Stephen linked to Christopher Sessum's excellent account of visiting a school doing project-based learning. My current interest in this topic stems from my thesis work, which is partly dealing with how people choose interesting projects (through learning goals). What if curriculum wasn't pre-defined and people could choose what (and how) to learn?