Many people at my work have a nerf gun or two hidden away inside their desks. We some times during breaks or after work, we would have a nerf war between cubicles. Or we would have a target practice session during lunch. The most popular nerf gun is the Maverick. They are small enough to hide in a desk drawer. They're also easy to swing around while you're dodging other darts. With the correct mod (instructions here), they are also easy to reload, making them quite ubiquitous around the office.

For heavy duty firepower, we have a Raider Rapid Fire (right picture) and the Vulcan EBF-25 Blaster, a fully automatic dart cannon. They are less mobile, and it's a pain to reload either. But in the heat of battle, a fully loaded one can be the difference between victory and a white flag.

All these guns are no good if you run out of ammo. So stock up with a few of ammo boxes. Just make sure you don't litter the whole office with these darts in every corner!