This one is going to have to be developed by your own interest. I am not sure there is a stock answer to this topic because all speeches are driven, to a great extent, by what would connect with the audience and what connects with the speaker. It is because of this need for connection with content that I am not sure "listing" topics for the speech can happen. Yet, I do think that Buddhism gives you a wide array of options within which some level of connection can be forged. Exploring these topics might be interesting for you and also interesting to your audience, providing information and an opportunity for reflection to emerge. One interesting element of Buddhism would be to discuss how it grew out of Hinduism, and that the Lord Buddha is seen by many as an avatar of the Hindu God Vishnu. This might be something to explore as there is a very close connection between both Hinduism and Buddhism. Additionally, I think that much can be harvested out of how individual the Buddhist practice of religion is. There is little in way of formal church services, but more along the lines of meditation and reflection within the individual. The lack of a "creator God" is also something that flies in the face of many of the world's religion and this might be another topic to explore. I think that one can find much in way of interest in the exploration of the Tibetan people and the role that Buddhism plays in the history of Tibet and, in particular, the Dalai Lama. Finally, investigating how Buddhism has been appropriated by the West is something that is really interesting.