Controversial topics are the best ones to choose, since there will be a lot of information that you can dig up to support your side. You can either choose a topic that's controversial and personal, or one that is on a more universal, global level. For example, you can discuss a medical issue that you yourself experienced, or something on a larger scale, like the truth behind organic products.
You'll have to choose a side that you're going to defend and promote. You can go the easy route and choose the side that most people take and that you know you'll be supported on by your audience. Or you can challenge yourself and choose the other, less popular side of the argument, and test out how persuasive you really are by how many people agree with your point of view once your five minutes is up.
Since time is limited, you have to make sure to get both parts of the speech in. You'll need to provide solid evidence that supports your take on the issue, including facts and figures to make your speech credible. You'll also have to include some creative information that will express your opinion and appeal to the emotions of your audience.
Fun topics to write a persuasive speech about include anything that has to do with pop culture and Hollywood; your favorite anything, like food, music or fashion style; or relationships. Remember, persuasive speeches don't have to be completely serious. You can take a lighthearted topic and write a speech on that too.
Topics on the more serious side include organ donation; recycling and green living; illegal drugs and steroids; and financial matters. Some serious topics have only one side that you'll probably want to argue for. For example, it may not be wise to argue for drinking and driving; the odds of you persuading anyone to see your side on a topic like that are slim.