Magic Bullet Editors has a nice preset filter called suprisingly "Night Time" that does a very nice job. Make sure your original footage is well exposed before applying this filter. Otherwise you can tweek it on the post gamma.
Phil, when you shoot with an DFN filter, shoot with about a one-stop underexposure from the UNFILTERED settings (you'll need to experiment to find what you're looking for).
Use the Cool Day-for-Night for a blue moonlight.
Monochrome Day-for-Night is used with subsequent color timing to create a more "silvery-moon" effect.
It is also important to make sure auto white balance is off.
Try not to shoot any sky, and backlight whenever possible, and obviously, don't let any shadows into the shot.