Clickbank can tell you what is hot if you sort their products by gravity or popularity. Keep in mind that very popular products have a tendency to "burn out"; they often only sell well for a few weeks.
This is most common for products in the "make money" niche. Products in the health and family categories tend to do better over a long period of time.
Products that have very high popularity also have a lot of competition. Unless you are prepared to take on some of the biggest marketers in the industry, you'd best start with products that have gravity of 50 or less.