what kind of brand do you have? your promotional items should match the market you're after just as much as your shirts, eh? ideally, the item should be seen by other people if it's a brand. if you're selling a service, perhaps something like a refrigerator magnet. do you have a logo you can riff off of? what's the name of your business/brand?
there are a gazillion things you can have imprinted pretty cheap, but that's not to say it's appropriate.