Markovic, Carroll, Diouf, Balotelli, Aquilani, Downing......the list is quite long.
And that's making some attempt to bring the amount of money paid into the equation, too.
Taking fees into account that's a pretty accurate list IMO.
Otherwise, for sheer awfulness I don't reckon any of them come close to poor Nicky Tanner, the guy who had previously been nicknamed "Whoosh" by supporters at Bristol ******* Rovers referring to the sound the ball inevitably made when Tanner hoofed it forward. Jan Molby was once asked who the worst player was that he ever played with. His answer: "Nicky Tanner. He was shit. He somehow managed to come in to training each day and be worse than the day before."