We all use Wikipedia, but if you want something authoritative and reliable, Britannica® Academic is a great option. Like all encyclopedias, this source is a good way to find background information on a topic.
CQ Researcher is a great source for information about current events and controversies. However, it also has some useful historical information, usually about political events (ex. U.S.-Iran relations). We recommend this source when you're having difficulty coming up with a topic. It's also a good tool if you already have an idea, but aren't sure what direction to take.
This source is very similar to Opposing Viewpoints in Context - it's a good place to look for information on controversial issues.
Use these sources to focus your topic, build a vocabulary, and find additional sources as you begin your research.