The new song is called "5x10" and Arashi wrote the lyrics.
http://www.johnnys-net.jp/j/artists/...llthebest.html
And disc three's track list has been revealed.
Disc 3 tracklist
01. COOL & SOUL
02. Yes? No?
03. ONLY LOVE
04. Natsu no Namae
05. Oh Yeah!
06. Re(mark)able
07. Boku ga Boku no Subete
08. Still...
09. Be with you
10. Subarashiki Sekai