If you love browsing in bookshops then I cannot recommend the 6th arrondissement enough. If you step away from the rather expensive -but très chic nonetheless- Boulevard Saint Germain, and move into the little streets towards the Luxembourg gardens (going the other way, towards the Seine, will land you in art gallery land), you might just come across the Village Voice.
www.villagevoicebookshop.com
I always run past it when I am on my way from one work to the other. Especially interesting are the events it has to offer its predominantly Anglophone clientele. Next week, for example, Dan Chaon will be reading from his new novel Await Your Reply.
It's what I love about Paris...move a little bit off the beaten boulevard and you will be rewarded.
Love,
Mustard