The big advantage of custom promotional products is that they can be integrated into the daily life of your customers. When you brand a product that is functional, like a pen or a USB drive, your customers will have your logo repeatedly show up as they go about their business.
The trick is to understand which products your customers use regularly. For example, if your market is athletic, you may want to brand sporting goods or water bottles. If your audience is in the tech field, mouse pads and flash drives with your logo may be appropriate. Find your promotional niche and make it work for you.