Critical system and how they go wrong (should be plenty of stories on the net). Most fun. We had lectures in uni about such things as the airbus (loads of bad things there), the ambulance phone system (oh dear), the US missile defence system (DEFCON thingy and problems with the moon etc), oh and nuclear weapons with electrical storms. Loads of fun
Oh and angle the talk to the idea about bad programming. Which most of it was. Ambulance phone service was the best (999/911 phone up for medical aid). They made the new system handle something like twice the average of the old one. Unfortuantly this average is massively exceeded now and again. So they shoved it live (and didn't run in parallel with the old one - just shut it down), and apparently completely froze the service because it couldn't handle when things got busy. A few people died from that one....
Cheers
I am 99% probably lying in bed right now... so don't blame me for crappy typing