It's always good to check out what's happening in Fondation Cartier. They have lots of really good exhibitions of modern art, and the gallery itself is very beautiful. Perfect for seeing works you already know as well as discovering new artists and inspirations.
Great place to start a day with a cup of coffee from the best roasters in the city, to eat lunch, to have an aperitif with your friends and to listen to a jazz concert every weekend.
This is another artistic centre that opened recently, this time housed in a former 19th century music hall that later became an indoor roller coaster attraction (yeah, really). The temporary exhibitions can be hit or miss, but I like hanging out in the free, open-to-all library on the first floor where you can sit in the futurist media pods and flip through the latest arts, culture, music, design and architecture magazines. Their shelves are also filled with a growing endowment of books which seem to be acquired according to the theme of the aforementioned exhibitions. Internet access is available on a dozen or so PCs (or via WiFi on your own machine) and for gamers, there are a few consoles connected to largish plasma screens. The café upstairs, with its classic baroque meets retro-futurist interior, is a sight to behold.