In my lifetime, the worst signing Villa have made was Bosko Balaban. He was a (Croatian?) striker bought for 6 million in like 2002/2003, and he was so bad that his contract was terminated after playing only 8 league games. He never scored a goal for the club.
Emile Heskey is another one. Martin O'Neill was offered Falcao for 5 million in 2008, but instead O'Neill decided to sign Heskey to give us the firepower needed for Champions League qualification. Needless to say, we never did make it to the Champions League, despite Emile's best efforts.
Who are the worst signings / biggest flops in your club's history?