Im suprised this hasn't been posted yet, unless I searched wrong. Sorry if it has. On these pages are the best of the best of super monkey ball 1/2 videos for ALL levels. I recommend you take a look, as some of these records are just amazing.
SMB1 - http://server1.vortiginous.com/smb/smb1/
SMB2 - http://server1.vortiginous.com/smb/smb2/
The person with the most of the records is this guy called packattack. He must have alien-like reactions, and you'll know what im talking about when you see this guy in action. Just take a look at these two videos, especially the first.
As for anyone who hasn't played this game, staying on the smallest path is INSANELY difficult. Some of these records look tool-assisted they are so good.
edit: Also, here is a really good highlight reel that shows off some funny and amazing runs of the game done by someone called SmilingJack13.