The UC Berkeley Post-9/11 Foreign Policy Class had a good lecture(the one from 9/17) by Louise Richardson on the motivations of terrorists. Much clear thinking about a topic that receives too little. A complimentary podcast can be found in the same class a year ago when they had Robert Pape speak(2/16 lecture) about suicide bombing in particular.
The critical point I think is that terrorists are not speaking to their victims- they're speaking to someone else. A lot follows from that.