Psychology is the study of human mentality and behavior. There are many topics to choose from under the subject of psychology, so you should be able to find at least one that interests you enough to research and give a speech. Addiction is a relevant topic in society, so are bullying, anxiety and the effects of stress. Choosing a relevant topic will keep your audience interested as you give your speech.
If you enjoy reading books and sharing what you know about different authors or certain, you might considering delivering a speech about literature. You might choose to educate your audience on the authors who were involved in the Transcendentalist movement 19th century, or the basic structure of a mystery or fantasy novel. Literature also involves poetry, so you might educate your audience about Shakespearean poetry.
Economics is another relevant subject in most peoples' lives, and there are a large variety of things to talk about in this area. You might do an educational speech on the major differences between capitalism, socialism and communism, or focus on a competition between two companies within the same industry (such as Ford vs. Chevy or Nike" vs. Adidas). You might also do some research and inform your audience about the current stock market trends.
Focusing on the subject of biology will give you a wide variety of different topics. Biology is the study of living organisms, so you might teach your audience about the parts of a cell, or how a plant absorbs carbon dioxide and emits oxygen. You could choose a topic that is in the current news, such as a disease that was discovered or an animal that is becoming extinct.