Here are January transfers that made a big impact for their respective teams.
The January transfer window is generally known for panic buys but these 10 transfers prove clubs can strike gold if they have a proficient scouting network.
No list is ever exhaustive, so don't hesitate to comment below with your own examples.
There were concerns when Clint Dempsey joined Fulham from the New England Revolution in the 2007 January transfer window for £2 million.
While he was considered one of the best players in Major League Soccer, he had never won the MLS MVP or Golden Boot award, so would he be able to make the step up?
Yet the upside Fulham saw in Dempsey came to fruition after hard work and dedication.
"Clint Dempsey always made the difference," then Fulham manager Martin Jol said last February, as per Matt McGeehan at The Independent. "I feel if Clint Dempsey hadn't been here over the last three or four years, we could've ended up with a real problem."
Now he has the chance to bail out Rene Meulensteen, Jol's successor, as Fulham fans hope Dempsey, on loan from the Seattle Sounders, can find his scoring touch again.
It has been almost a decade since the 2004 MLS SuperDraft.
Seven players including Freddy Adu were drafted ahead of Dempsey.
Yet he is the one who's had the most successful European football career, is a star for the United States men's national team and is on a lucrative contract with the Sounders.
Klaas-Jan Huntelaar never got a chance at PSV Eindhoven.
He had to bide his time with De Graafschap and AGOVV.
After scoring 40 goals in a season-and-a-half at Heerenveen, Ajax signed Huntelaar in the 2006 January transfer window for €9 million.
Three years and 105 goals later, Ajax made an €11 million profit by selling Huntelaar to Real Madrid.
What a master stroke of a decision from Bayer Leverkusen to sign Dimitar Berbatov in the 2001 January transfer window.
During that period in the late 90s to early 2000s, Leverkusen were the Porto of the Bundesliga: Lucio, Michael Ballack, Ze Roberto and Juan were just some of the world-class signings Leverkusen made.
Berbatov went on to score 69 times and created 32 goals in 154 Bundesliga games.
Before Mario Gotze, Robert Lewandowski and Torsten Frings, Freiburg's Sebastian Kehl was in the middle of a dispute between Borussia Dortmund and Bayern Munich.
When Bayern suggested transfer improprieties, Dortmund snapped back.
"We are not the ones who throw cheques at players who are contracted to other clubs," Dortmund sporting director Michael Zorc said, as per Frankfurter Allgemeine Zeitung (h/t Sky Sports). "Kehl has said to us quite clearly that he has not given Bayern an oral or written agreement."
At the time, Dortmund beat out Bayern in successive January transfer windows to a world-class prospect.
In 2001, it was Tomas Rosicky. The next year, it was Kehl, who has since played over 300 times for Dortmund.
"If I have to walk to Manchester United to play there, I'll walk," then Spartak Moscow player Nemanja Vidic said in December 2005, as per Nemanja Vidic: The Biography by Frank Worrall.
United completed his signing for £7 million in the 2006 January transfer window.
He was only £3.2 million more expensive than what Chelsea spent on 16-year-old Slobodan Rajkovic, a compatriot of Vidic.
Rajkovic was never given a chance at Chelsea while Vidic is now a five-time Premier League winner and a UEFA Champions League winner.
Early on in Branislav Ivanovic's Chelsea career, he was considered a monumental failure.
He arrived from Lokomotiv Moscow for £9 million in the 2008 January transfer window amid big expectations yet wasn't even fit enough to play Premier League football.
Well, that was the opinion of then Chelsea manager Avram Grant which almost led to Ivanovic packing it in.
"Maybe I was thinking [about quitting] but that was two years ago," Ivanovic said in 2010, as per The Guardian. "I have no ill feeling towards Avram but at that moment I was really angry."
Guess who helped Ivanovic through the hard times? Andriy Shevchenko.
For Shevchenko, who was Chelsea's Fernando Torres before Fernando Torres, to lift Ivanovic's spirits up is a testament to the Ukrainian's character.
It is something Ivanovic will never forget, as per The Guardian:
He [Shevchenko] really helped me. He tried to give me confidence. He told me about the style of play in England, what I had to do as a defender and where I could improve.
It was a difficult period for him, too.
He had been outside the team, he was also injured, but he wasn't just thinking about himself, he was thinking of me too.
I can only say a big thank you to him for everything he did because he helped me become prepared for when I would play.
Ivanovic has since won the UEFA Champions League, a Premier League title, a UEFA Europa League and three FA Cups as a Chelsea player.
Football has had Mozart Santos, Thomas "Mozart" Broich and Tomas Rosicky, who orchestrated play on the football field as well as Mozart used to compose classical music.
Rosicky, a midfield virtuoso, could have been a Bayern Munich player but opted to sign with Borussia Dortmund from Sparta Prague in the 2001 January transfer window.
Dortmund were loaded up front: a goal-scorer in Marcio Amoroso, 6'8" Jan Koller, the dazzling Ewerthon, oh and throw in Rosicky's playmaking.
The four combined for 44 goals and 33 assists during the 2001-02 Bundesliga season.
As soon as Dortmund encountered financial problems, Bayern Munich legend Franz Beckenbauer urged his club to sign Rosicky.
"I can well imagine Rosicky starring for Bayern in the long-run," Beckenbauer wrote for Bild (h/t Sky Sports). "We had been keen on him once, but then pulled out of the transfer poker."
Rosicky's body started to break down and he went from being on top of the world to just another midfielder.
From time to time at Arsenal, he conjures up Dortmund-like brilliance.
Dortmund left attacking midfielder Marco Reus remembers Rosicky's impact, as per Donald McRae at The Guardian:
My idol was always Tomas Rosicky. He used to be phenomenal. He had such a good eye for an opening and knew where his team-mates were, and he was so quick.
Rosicky had great technique and was so intelligent and mature even though he was still young at Dortmund.
I copied everything about him—right down to his sweatbands. He was so unlucky he had bad injuries at Arsenal because, otherwise, he would be one of the world's best players.
When Luis Suarez signed from Ajax in the 2011 January transfer window for £22.8 million, Liverpool were receiving a diver, a biter, a troubled individual but the most outstanding Eredivisie talent since Ronaldo Luis, who was exceptional at PSV Eindhoven.
Suarez had scored 49 goals during the 2009-10 season for Ajax, so Liverpool were willing to accept his flaws as a human being.
It hasn't been easy for the Reds but their persistence and blind loyalty to Suarez is paying off.
With 20 goals in 15 Premier League games this season, Suarez won't factor in the 2013 FIFA Ballon d'Or but will be a contender for the 2014 Ballon d'Or.
How did Manchester United sign a left-back with world-class potential in Patrice Evra, who had competed in the 2004 UEFA Champions League final for Monaco, for just £5.5 million?
"We have been monitoring him [Evra] all season and it is fantastic he is joining us," then United manager Sir Alex Ferguson said, as per BBC Sport. "He is a good age and he is still developing as a player, which is always exciting."
This was January 2006 and eight years on, United have expended Evra's usability as a top-flight left-back.
In return, he has played a part in five Premier League winning seasons, lifted the Champions League trophy and appeared over 360 times for United.
Ivan Cordoba was a pint-sized, hard-nosed and passionate defender for Inter Milan.
He and former Juventus hardman Paolo Montero would routinely compete for the worst tackle of the year award.
While Cordoba committed some x-rated tackles, it was always fun to watch him leap over taller players to win a header.
Cordoba justified Inter management signing him from San Lorenzo in January, 1999 by playing 455 games for the Nerazzurri.
He won five Serie A titles, four Coppa Italia titles and was a member of the 2010 UEFA Champions League winning squad.