Unlock "Celebrate And So In Love" - Fail First Song
Unlock "Gentle Stress" - Fail Oni Mode
Unlock "Max 300" - Pass extra stage or play 100 songs
Unlock "Candy" - Pass encore extra stage or play 200 songs
Unlock "Drop The Bomb Remix" - Pass Hardcore or play 500 songs

To list all the songs in alphabetical order on the song select screen, hold LEFT and RIGHT on the pad and press start. This trick works for every DDR, including the arcade versions.