The World Book Encyclopedia continues to be one of the best general encyclopedias you can find. It covers just about everything you could want for a school project and has lots of pictures, graphs, charts, timelines, maps and outlines to go along with the written information. A new updated and revised set is published every year and the London Public Library buys the newest one every year especially for elementary and secondary school students. It is that good! It is organized alphabetically and comes in a total of 22 volumes. It has a very good index (the last volume of the set), so be sure to look at the index if you can't find what you are looking for; it will direct you to the correct volume.
Looking at a good encyclopedia is a great way to start researching a topic. It will give you an excellent overview and after you know more about your topic, then you can start to do more in-depth research with books, newspaper and magazine articles, and websites.
The World Book Encyclopedia and World Book for Kids are available online but only through the London Public Library's website because they are not free databases; the Library pays for a subscription. But all you need is a London Public Library card and you can use it 24/7 from home.