Every now and then, I download the Oricon Top Twenty (you can find the torrent on Tokyotosho) and this song was on it too. You can't escape it.
So I give up. My only hope is to inflict it on you as well. It's like Ring, in a way.
Gake no Ue no Ponyo - Gake no Ue no Ponyo (Main Theme)
(I also downloaded a handful of The Smiths stuff recently, so you can imagine what that's doing for my mood. I don't suppose anyone would have any Weiss Kreuz songs lying around, particularly the solo stuff and duets? I used to have pretty much every song on CD, but I left all my CDs in Britain and my MP3 player subsequently died.)