#7 Raul | Real Madrid to FC Schalke (2010)
Raul is one of the greatest names to have graced the beautiful game, acquiring legendary status during his time at Real Madrid. The striker scored 323 times for Madrid in 741 appearances, winning six La Liga titles and three Champions League medals in an illustrious 16-year stint at the Santiago Bernabéu.
Raul became a free agent in the summer of 2010 and had the option to choose from a host of top European clubs. He eventually moved to Schalke as a 33-year old, but there were doubts about his ability because of his age. But the Spanish legend showcased his class once again - this time in German football - scoring 40 goals in 98 appearances for the Bundesliga club.
The Spaniard helped Schalke lift the German League Cup and the Supercup titles in his two-season stint at the Veltins Arena.
#6 Michael Ballack | Bayern Munich to Chelsea (2006)
Michael Ballack departed Bayern Munich as a free agent in 2006, choosing to shift base to Stamford Bridge, amid interest from Manchester United, Real Madrid and Inter Milan.
Chelsea were known to splurge a lot, especially in the early days of Roman Abramovich's reign. But the Ballack signing turned out to be one of their best transfer moves, one that didn't cost the club a penny.
The three-time Bundesliga winner and three-time German Player of the year continued to add to his illustrious trophy cabinet in four successful seasons at Chelsea. In 167 appearances for the Blues, Ballack notched up 49 goal contributions (25 goals and 24 assists).
Ballack left Chelsea in 2010 for Bayer Leverkusen after winning two Premier League titles, one FA Cup and one League Cup.
#5 Paul Pogba | Manchester United to Juventus (2012)
Paul Pogba left Manchester United on rather unsavoury terms, after failing to impress Sir Alex Ferguson. Controversially, the Frenchman let his contract run its course and left Old Trafford on a free transfer in the summer of 2012.
Juventus did have to pay a minimal compensation fee, but that was well worth the 34 goals and 40 assists Pogba produced in 178 appearances.
Pogba's four years at the Allianz Arena elevated his reputation from a promising youngster to one of world football's best midfielders. The Frenchman also won four consecutive Serie A titles during his time at the Italian giants.
Interestingly, four years later, Manchester United dished out $115 million for his services after letting the player leave for free. Suffice to say, Pogba's second stint at Old Trafford has been a bit of a mixed bag.
#4 Sol Campbell | Tottenham Hotspur to Arsenal (2001)
In one of the most controversial moves in the early 2000s, Tottenham Hotspur captain Sol Campbell shifted his allegiance to Spurs' arch-rivals Arsenal.
Campbell had initially suggested that he would stay on at Tottenham Hotspur, so the Lilywhite faithful rightly felt betrayed when he moved cross-town to join Arsenal in 2001.
Despite all the talk surrounding his 'betrayal', Wenger signed Campbell solely based on the player's defensive acumen.
The Englishman was one of the best centre-backs in world football at that time and played a key role in Arsenal's 'Invincibles' who went unbeaten in 49 consecutive games.
After 12 years at Tottenham Hotspur, Campbell spent his next five at Arsenal, winning two Premier League and as many FA Cup trophies.
During his time at Arsenal, Campbell helped the Gunners keep 51 clean sheets in 211 appearances. He left the club in 2006 but returned for a final one-year stint in 2009-10.