Apart from the fact that they are ridiculously expensive, clubs in Tokyo are otherwise quite fun to visit and hang out at. In contrast, Izakaya (居酒屋) is a more common and affordable place to get together and hang out in Japan.
Shibuya, Roppongi, Takadanobaba, etc are places full of clubs. Been to a few of those, some of them have very unique interior design. (Yipes, i realised that i dont have any nice photos to post here, cos i seldom bring my camera to clubs. sob.. sob... what a waste..)
The crowd is usually international.
Some new friends I made in a club:

Thai, Jap, Indian, and Me

Nice exterior design:
This particular club even had a live percussion performance: