M Flo + SOL - Go Crazy (Lyrics video)
M Flo + Ayumi Hamasaki - My Way (sound only, short version)
M Flo + Daoko - IRONY (Sound only, short version)
edit:
The official website has provided previews for all the songs. Check it here
Source: mflo10yrs
I like Yoohei Kawakami's voice. And I think "Go Crazy" is available in iTunes right now.
Add that previews bit. And from the preview...I think I like "Neven" better :3