HD Camcorders

Almost no digital camcorders will perform "well" in such a situation - they like light, and you will get a very underexposed, noisy picture. To rectify this, either record under a lot of lighting - I don't know what the nightclub in question will have - or bring your own lighting to compensate.

I would use a light with it. Doesn't matter which camera you buy. I once filmed with a SONY HDV FX1E and I used a lamp with it. When you watch shows with camera's in club (e.g my sweet 16) they always use lights with it. It will look weird for the people that are there, but on screen it will look really normal and clear. So always use it, even though people won't like. Because else it will be useless.

You can get a LED light with 50 dollars, but I would go for something more expensive/durable.

I'm talking about the close-ups. You're little camera light won't effect overall shots ofcourse.

The Panasonics you mention are particularly poor for shooting indoors in minimal light. Look for something with a larger sensor - though this may well mean spending more money. The Canon HF100 is targeted at a similar market, isn't too much more expensive (if you can still find it as it's been replaced by the HF200, which is not as good at indoor video), and is better than the Panasonic SD5 / SD9 / SD20 indoors.

That said, you'll still want to light everything. Video likes light.

I've videotaped in night clubs and used a lot of tiny little led lights and candles and other things. Spread light around that looks like it should be there. If you're filmming a conversation at the bar or at a table you can use a small battery driven light panel with a napkin over it - the light looks great.