I can't claim to have a magic formula, all I know is what I like.
First, you need a tripod, since I find an exposure time of 3s to 5s is about right. The ones in the slide show above are 3s, in the one below they are 5s
You need to consider that you are painting the sensor with light, so after some trial and error, here's my suggested settings:
Image quality / type: raw if you can, then you can try to recover some blown highlights
Shutter: 3 seconds to 5 seconds depending on choice
lens: for these I used a 12-24 on my D300
keep taking photos!