Clickbank has a huge selection of products, probably one of the biggest databases, you'll surely find something to promote. It's also very easy to get started with Clickbank. The downside to Clickbank is that it is the most used so promoting some of the products may feel like they are saturated or don't perform as well because a lot of other people have already promoted it. However since they have a huge selection, you'll find something of interest to promote.