As in writing, citations provide evidence that experts support your statements. This makes your speech credible. Oral citations give proof of well-researched content.
Cite your source whether you are quoting or paraphrasing. Protect yourself from PLAGIARISM always.
Include a slide at the end to list all the sources you used. It may even be helpful to provide a handout with these!
Give some variety to your oral citations: "According to...." "This is supported by...." "John Doe says...." "As Jones states in his paper...."
Don't forget to introduce the person the first time, though! "Psychologist Jane Doe has suggested... Doe also reports..."
Who should you namedrop?
If it's someone who did the original research and/or is an expert in the field, go for it.
Is it just a journalist reporting on what someone else did, and any news source could have given you similar info? Leave it as a parenthetical. At best, you'd state, "According to The New York Times..." with a little (Doe) parenthetical on your slide.