Gale provides a good list of topics for student during the brainstorming days if you choose to make this research free choice.
One of our databases list very hot topics on their landing page. They are argumentative nature and provide
Similar Databases do the same
If you want to limit choice to inhibit students being overwhelmed, provide them with a list that they can use instead of topic searching.
Once they have chosen topic, have them brainstorm with scaffolds below.