Photography: Neutral Density Filter

[copthat]

I have my eye on getting a Neutral Density Filter for my Nikon D3000 and I was wondering if any of you guys have one and use one, and if so are they worth it? Which one do you have? I like doing long exposures and I can't find the time to get out at night as this is the only time to do them, unless you have a Neutral Density Filter.

It would be much appreciated if you guys could give some feedback on what brands are good etc.

Thanks.