Over-rated: Flamethrower, Thunderbolt, Ice Beam, Psychic, Earthquake, Shadow Ball
Under-rated: Flame Wheel, Shock Wave, Icy Wind, Dig, Aerial Attack
Basically, if the base power is higher than 80, it is considered over-rated, if lower than 80, it is considered under-rated. Analyzing the base power and accuracy solely is the way to determate whether a move is over- or under-rated, but the effect has some important role in the defining it as well. Avalanche, for example, which is a move with 60 as power base. It'll cause double damage if user is attacked in the turn it is used, in that case, if user attacks last, then its power will be 120, which is far from being a under-rated move. Anyways, this is something that requires effect and will not happen in every circunstannces. That's why when you compare under and over rated moves, you analyze the power and accuracy solely, not the effect.