To be super helpful, make sure you post a link to the song so we can listen to it (if you can find one) and/or some text lyrics to read to go "A-HA, I see it, that Britney Spears song is totes Aizen/Gin/Tosen threesome."
"Fallin" by Chris Brown totally makes me think of Ichigo, especially up to the most current manga chapters. (I know, kind of a douchey singer to start off with but the song just fits soooo well!) It really expresses his inner struggle, but I don't wanna say too much and spoil anyone so I'll leave it to you guys to read and/or listen and judge for yourselves.
Listen here: http://www.youtube.com/watch?v=c_CjrPUITgs
Read the lyrics here: http://www.lyricsmode.com/lyrics/c/chris_brown/fallin_down.html
I've got more songs in mind than just one but I thought one was a good start, heh. Oh, I usually use www.azlyrics.com for lyric links because they have a lot less crap on the page but this song has a lot of inaccuracies over there (it's all user submitted, so it happens).
Your turn, go! :D