Gearing up for an exhibit and at a loss on what to give away? Consider usable ones over cute, non-usable ones any day.
Sure, pens and mugs may seem already boring and every possible exhibit booth give these away. But those who do get it are sure to use them, so your adverts in that cup wouldn't be wasted. Besides, you can make those promotional pens funky, cool, hip, attractive and all kinds of interesting anyway.
Get those that offer two to three color inks. Get those that can be used as laser pointers or mini flashlights as well. Get the scented ones, or those that write in gel-type inks (or even those that are in out-of-this world color like silver or gold). Of course, people are still more likely to use black-colored ballpens so you might want to just stick with the old and trusted.