What are your interests? I’d recommend going with something you really enjoy. Contrast the iPod with previous MP3 players. What is the difference in Sting’s musical style today from what he had when his group was first topping the charts? What differentiates Australian Rules Football from Rugby (Union)? What caused the USer civil war, versus what caused the Spanish civil war? How did the invention and development methods of Tesla and Edison differ? English and Chinese are regarded as the two hardest languages for a foreigner to learn — what features of each language make it so difficult?

Do any of those strike your fancy? If not, what sorts of things do you enjoy talking about and learning about?