Actually, Sasuke's rope untying "jutsu" was only mentioned in the anime. In the manga he just says any ninja knows how to untie knots.
I don't think Sai's moves are really that bad. They're perfect for collection data and spying, and we haven't really seen him in a serious fight yet.
TenTen wouldn't be so bad, if the manga didn't have a bad habit of making weapons completely USELESS. I'd have to say Ino's body switch jutsu. It's just so lame.