Here are some examples of successful promotional items: t-shirts, coffee mugs, flying disks, pens, pins, keychains, corkscrews, letter openers, fly-swatters, jackets, hats, sweatshirts and book-ends.
One can have a general promotional item or an item for a specific event. Generally, the more visible an item, such as a t-shirt, sweatshirt, or jacket, the more effective it is. They can be given away or sold.
Check the yellow pages under Advertising-Promotional Packages or google "Promotional Products" to find manufacturers.