There are so many things happening in Paris every week. Given the clubs, museums, theatres and other venues, it's not hard to believe. Since there is no way to keep up-to-date, it's best to go right to the source.
The best source of current events in Paris is Pariscope. Although it's only available in French, It is still a great resource. It's also a good way to learn a little French!
But if you are not up for the challenge, Paris Update is also a
good resource, including links to the websites where events are being held.