Certainly there are many fine boulangeries in Paris but for me, the perfect baguette can be found at Eric Kayser (on Rue Monge). You must ask for the Baguette Monge, and if you have good timing, it will be still warm from the oven.
They are a little over 1€ - what a bargain.
For a little piece of heaven, step outside, pinch off the top,
and take a bite while the steam fogs your face.
Baguette Monge, Eric Kayser
8, rue Monge (and other locations in Paris)