We've created a library of free people plus links to free and affordable stock photo sites.
The best person to show in your marketing is you. Set up a shoot with a professional photographer and get a full set of photos (make sure you get transparent backgrounds). If you're not comfortable with yourself, get a set of stock photos.
Check out these free and paid resources
My favorite royalty free stock photo site that offers beautiful HD photos, including photos of people.
Another site with a great library of royalty free HD photos.