Your local library usually has a good variety of guidebooks, although they aren't necessarily the most current. I usually check out an armload of them, and then use amazon.com to order my favorite for the trip. I have actually taken the library book with me, but usually prefer ownership so I can mark them up.
And I usually end up buying the Lonely Planet one. I like the maps and specific directions and walking tours. Consider one on just Paris too. The city specific ones are nice light slim little things for traveling.
Romelle