Start at the Pompidou Centre bookshop and work out from there into the Marais

Also, you've got to head out to La Defense metro station. There are a lot of cool modern buildings there.

Very obvious one but...you should go to Colette. Great store with all sorts of books, mags, clothes, food, design stuffs...
colette.fr

Well it depends what books you r looking for?
Here are some places to go:

Eyrolles Bookstore at bd St.Germain in 75006.
http://www.eyrolles.com

Check out this website:
http://www.studio002.com/index.html

Thanks everyone posting here. Thanks for your help! I actually will be looking for graphic design books, subculture mags, architecture stuff, as well as some cool clothing (t-shirts and so...). Also those kind of little autor-books (those that are almost hand made...)
In fact almost every kind of visual trend related to graphic design and communication...

I think, the places named here in your posts are a good starting point, aren't they?

Big thanks, and dont stop posting!

Love!

I was actually in Paris about a week ago, and besides colette, visit the palais de tokyo. Its a contemporary art museum. I believe its the 13arr. Also worth a look, if youre into parfum make time to visit the commes des garcons parfums shop near le rue de saint honore (next to colette). They have their bi annual series of perfume and they are excellent, definitely smell the sweet series, and I was fond of the synthetic scents as well.