Just a 15 minute walk from the Louvre, this cute, cosy bistro is in a central location yet somehow always manages to have a free table and super fast, friendly service. I loved this place because they serve some very good traditional french dishes (I would recommend trying the onion soup or confit duck in particular) at a fraction of the prices you would normally see in city centre restaurants.
Once when I went there they even had a 10 euro steak as the special, and I have never been able to finish off a full plate there as the portions are so geneous. Wine and alcoholic drinks are also pretty affordable there and the staff a lot kinder than at the more touristy locations. They even have some good irish coffees and cocktails.
Afterwards, you are in a good location to go out looking for bars and clubs, and there are many close metro stops.