I think Eiko Shimamiya's Ozone receives horribly little recognition. Nobody seems to even remember it exists, but I think it's one of the most beautiful songs she has ever made. It goes from depressing to uplifting and back with the excellent combination of piano and Kazuya Takase's signature synth strings carrying it through and Eiko's emotional vocal performance just crowning it. Not to mention that it has beautiful lyrics to boot.
And yet, it wasn't too long ago that no one had even bothered to upload this song to Youtube, which made me really sad.