I have to agree with some of the earlier stuff. Thus my choosing a different style for my choices...
Dearly Beloved, from Kingdom Hearts. So many versions of the song, all of them, I really like.
Reset, from Okami. The ending theme (as well as a final scene theme (there's another version, without the lyrics).
And finally, the two theme songs of Solatorobo...
And Then, To Coda, and Re-CODA.