I haven't seen "500 days of Summer" unfortunately, I heard it was really sweet and filled with vintage, or vintage-like clothes to die for. I've loved Zooey Deschanel for a very long while (I also love Emily her sister and Bones!) and recommend listening to 'She & Him' if you're into easy-going old-styled music. This is pretty much a feel good song and video. Enjoy.
The lyrics, aren't that easy breezy (even though they are very 50s styled (everything's very styled this post isn't it??)) and all I can say is: Zooey, I feel you honey.