The templates above have already covered email series, ebooks, and white papers, as well as different video content like webinars and documentaries. Besides those some other suggestions of gated content that you might choose to offer are:
Content upgrades – access to additional material
Demos/trials – a period to test out a product or service for free
Spreadsheet templates – save users’ time by providing a form with blank spaces to be filled in
Process documents and swipe files –  such as an onboarding template