Many free font sites aren’t necessarily where you want to go when you need fonts for work or an important presentation. Questions about quality and copyright abound.
However, if you visit Font Squirrel, you’ll find free fonts that are specifically free for commercial use. These free resources can help you add some design flair to your presentation. Just remember to load the font on the computer you will use to present. I generally do that by putting a copy into the folder with my presentation. That way it will travel with me and can be easily installed if needed. Try Font Squirrel here.