That really depends on what team you are, as a great buy for a Premier League team would be completely different to a great buy for a Blue Square North/South team.
Having said that, getting Davide Santon on a free has been very useful in my United save; but Toni Silva for free on my Basingstoke save was my best signing.
Got Olic for free, if that counts, player of the year in his first season for me at newcastle, and top scorer in the world... if that doesnt count then Andrea Poli has been a good signing to replace Tiote, i think he was about 5.5 mil
Abidal, 8 million half way through the second season
Tapped him up and nabbed him to replace Kolarov
Got in the team of the year and only came in january
Apart from that in my usual lower league saves I would say Kara, Jenssen, Laudrup are sensational signings
Eden Hazard, has a £30m value and is world player of the year now. Giuseppe Rossi and Thiago on free transfers. Wilshere for £2.5m, worth £11m now. Practically all of my signings are sub £15m, these are the ones I'm happiest with though, along with some star regens.
Gaston Fernandez or Luis Bolanos. Free transfer for Tenerife. Gaston first season grabbed 26 in around 40. I was pleased . Bolanos has an average rating of 7.51 in the first season and 7.37 in the second. Probably my better acquisition and his display kept me up in the Liga BBVA.
Just signed Mario Gotze on a free too and he'll join at the end of the season. Life on the island is good
Angelo Palombo - 7.5million from Sampdoria, season 2, 2 times
Was a monster in my Liverpool and Tottenham files. Fantastic anchor midfielder. My defense wasn't too solid, but this man just made sure no attacking play got into the final third.
1) Lucio (1.2million, 3rd season at 34)
2) Jan Chramosta (1.8 million)
3) Yuri Zhirkov (2.4 million)
4) Renan (2.6 million)
5) Macdonald Mariga (1.9 million)
6) Javier Orozco (750k)
7) Alan Dzagoev (2.4 million)
8) Harry Novillo (1.8 million, 1st player I buy on every game)
9) Nicolas N'Kolou (8.25 million)
10) Javi Garcia (4 million)
On my Wigan save, he was my best signing for £9,000,000 (2014/15). Just an all-round excellent player! But AC Milan snapped him up off me for £16,000,000, the bastards.
On my current save, I bought Fabrice Abriel for £750,000 and he's just on another level, old, but has had like 20 assists in the last two seasons. Also got Serge Aurier on a free at the end of 2011/12, excellent form so far this season, averaging 7.35ish. And another has to be Ronny Rodellin, paid £325,000 for him and he's now wanted all over europe with the highest offer being £6,000,000 but I rejected and he claimed he is happy to stay at the club. 17 goals in 19 games this season and still only 23.
Romelu Lukaku without a shadow of a doubt for me for £7.5 million in the 2nd season. He has scored more than 30 goals every season and is now my club captain at Liverpool. Can play upfront on his own, upfront with the support of a couple of inside forwards/wingers and is also great with another striker in a 4-4-2 using him as a taget man.
Also Kader Mangane for £11 million has been absolutely immense for me in his 4 seasons at the club.
Daniel Sturridge on a free in the 2013/14 season, helped my Newcastle side win the Premier League, or Luiz (a regen) for £2.1 million was aged 18, and he's been immense