**EDIT** Since this is perhaps restricted in some territories, it's the opening sequence for the anime Paranoia Agent. If you can track it down in your area, check it out, well worth a look.
This one has always stood out for me. It's this amazing blend of what SOUNDS like a really cheerful and upbeat, but....really isn't on a lot of levels. Plus the imagery, again, at first, seems really uplifting...until the frame starts panning out, and you start taking into account the little details in the shots. Each person's surroundings, how they're all just laughing....and laughing....and laughing. It's this fantastic contradiction, that encapsulates the mad tone of the show. Sadly the finale of the show totally shit the bed, in typical insane japanese anime fashion, but the first half or so, really solid, creepy, X-Files kind of bizarre. Plus I also just really enjoy the song. Fast drums, high vocals, long notes held to touch the sky, that's my kind of stuff.