Well I asked that question also so I did some research and I found a lot of websites that offer plenty of topics on google just by typing in science fair projects and the topic that I was interested which was electricity and I found a project on the proccess of electrolysis.
I have a good website for you regarding this topic, it provide many science projects. Just click on the link given below, you will find many science projects topics. click on the project you like. These science projects are easy to prepare.