Paprika
Where do I begin? In Satoshi Kon's latest masterpiece (if you haven't seen Millennium Actress you should) he answers the loaded question, "What if a research organization created a device that allows multiple people to interact lucidly within each other's dreams, when a corrupt insider hijacks the device, remotely forcing multiple people (only those who have already used it) into this dream world, which then begins to merge with reality itself (a deliberate attempt to throw societies "nighttime fantasies" on a literal rampage)". That's really only the beginning of it - there's a lot more going on here if you want to look for it. In the end, the story takes a back seat to it's jaw dropping animation. You would be hard pressed to find any animated film that comes close to touching "Paprika" in quality and style. The visuals perfectly touch on the scope of our dreams; they are both simultaneously funny, beautiful, saddening, and horribly frightening. It is not without it's inconstancies, but it's the type of movie you just have to sit back, enjoy every frame, and save the thinking for later.