Whether it's your own dog or the neighbor's, having to hear the booger bark all night is no fun. Try looking at it from Rover's point of view: It's dark, he's lonely and the sounds around him are either scary or stimulating. While no foolproof solution to nighttime barking exists, you can do things to try to make it stop.
Give banishment outdoors a second thought if this is your doggy. Canines are social animals, and living outdoors alone is bound to cause barking or howling -- just because he's alone and possibly scared. If this is your neighbor's dog, consider having a talk with the neighbor.
Build an enclosure to keep Doggie confined and make him feel more secure. Being outside doesn't have to mean being loose in the yard and exposed to the elements. Moving him to a locked kennel provides a safe place to sleep and may encourage him to do just that rather than being up and barking all night long. You can add blankets, toys or other items to see if that helps with the barking. If you're on friendly terms with the neighbor, you could suggest he does just that with his own dog -- if his is the one barking, of course.
Eliminate the cause of the barking if it's known. Some dogs bark when they see cats, other dogs or strange people walking by at night. If that's the case, building a privacy fence around the property might solve the problem.
Give your dog a distraction. Leave a small radio on near his sleeping area throughout the night. This will accomplish two things: make him feel less alone and help "cover" some of the other nighttime noises that might be causing the barking in the first place. Just make sure the volume is not too loud or you might also keep the neighbors and yourself up.
Buy an ultrasonic bark deterrent. This is a small battery-operated machine that emits a high tone anytime a dog barks. Because the pitch is annoying and distressing to dogs, they should soon learn that barking activates the tone. Different brands have different ranges -- between 35 and 50 feet is normal -- so make sure you choose one that's appropriate for your situation.