Transfer: Millwall to Everton, 2004
Price: £1.5 million
Impact: Since Everton took a chance on the Aussie from the lower leagues, Cahill has scored almost one goal in every three games – an amazing record for a midfielder. Two years after signing for Everton, Cahill was one of 50 players nominated for the Ballon D’Or (European Footballer of the Year).
Money well spent? After just one season with Cahill, Everton finished above cross-town rivals Liverpool on the table: an achievement for an Everton fan worth more than any transfer fee.

Transfer: Leeds United to Manchester United, 1992
Price: £1.2 million
Impact: “The King” brought the glory years to Old Trafford. In his time with Manchestier United he won four league titles and two FA Cups, and established a culture of success that has made the club what it is today.
Money well spent? Before Cantona’s arrival, Manchester United had not won the English league title in 26 years. Since his arrival, they have won nine league titles in 16 seasons. Four months before Cantona’s transfer, Alan Shearer moved to Blackburn for a bargain fee, yet it was still three times what United paid for Cantona. Shearer would win just won league title in his career.

Transfer: Barcelona to Napoli, 1984
Price: £5 million
Impact: With Maradona in the Napoli side, the club won two Scudetti, was runners up twice, and took home the UEFA Cup in 1989. Were it not for Maradona, Napoli would still be one of many unfashionable Italian battlers with little claim to fame.
Money well spent? Thanks to Maradona, the club secured international confectionary giant Mars as their major sponsor. Their previous sponsor was Buitoni (“Homemade Italian Meals in Minutes”). Still, at the time £5 million was the largest ever transfer fee paid…

Transfer: Motherwell to Celtic, 2007
Price: £750k
Impact: Since arriving at Celtic, McDonald has scored in excess of one goal every two games. He has scored a winner against AC Milan and back to back league hat-tricks at Celtic Park.
Money well spent? In early March, Newcastle were reported to be interested in buying McDonald for about 10 times what Celtic paid for him. On-pitch performances aside, in terms of sheer gain on investment, the McDonald transfer has been money exceptionally well spent.

Transfer: Sao Paulo to AC Milan, 2003
Price: €8.5 million
Impact: The 2006/07 UEFA Champions League would have not have been won by AC Milan were it not for Kaka. The club should have won it two years before as well (were it not for an unlikely Liverpool comeback in the final).
Money well spent? Investing so much in an emerging playmaker with a history of spinal injuries was a risk. But Kaká has risen to become a giant of the game. The 2007 FIFA World Player of the Year just signed a new contract until 2013, stating “I will remain a Rossonero for my whole career”.