Are you hanging drywall, flooring or other tasks that require you to set fastener after fastener? If you are, you should check out the Bosch 18V screwgun. Talk about lightweight, efficient and making the job simple, the Bosch delivers.
With the SGH182 a user can drive home about 3,400 screws using a 4 Ah battery. Speaking of batteries, you use your existing batteries and just buy a bare kit to help save a couple of bucks or if you fancy a kit, they also offer a kit version. Almost forgot, this also has a brushless motor, which means longer life. As with other top drywall screwguns on the market, there is a lock on button for continuous work and adjustable Posi-Lok nose-piece. Speaking of continuous work, you can also buy the MA55 autofeed attachment so you can really pump out some work. You might be thinking this thing is pretty heavy, but actually it's pretty light. With a 4.0 Ah battery it only weighs 3.53 lbs.
If you are looking to hang some serious drywall and desire efficiency, speed, lightweight and just a tough tool, the Bosch won't disappoint you.