When it comes to achievements, I feel they mostly should either be games in their own right, or just awards for playing really well. So basically no grinding ones. So to this end:
Untouchable:
Play an entire song without touching any blocks. Minimum 3 minutes, 100 traffic congestion.
Laser Spectacle:
Collect a match of 21 blocks or more using all five colours.
Avalanche:
Cause 3 white blocks to hit the bottom row at the same time.
Grand finale:
Collect a match of 21 blocks after the final block of a song has passed.