Swansea - He was their for 2 full seasons these are the ones who I'd highlight as being the best and why:
2010-11
Neil Taylor - Free - Signed for Free went on to play 30 times in the Promotion winning season, then 36 times in the Premier League.
Scott Sinclair - 500k - He's worth a lot more now, He's scored 35 times in his 80 odd Swansea apperances and is now one of their most important players.
Borini - Loan - During his 3 month loan he became a crucial player in Swansea's eventual promotion scoring 6 times in 15 apperances
2011-12
Caulker - When fit was an ever present and You only have to ask Swansea fans how highly they rated him.
Graham - £3.5M - Most expensive signing Rodgers has ever made, 14 Goals in 39 games is a good return.
Vorm £1.5M I'd say his value is possibly between 7-10 times that now (I'm going OTT) but for £1.5m he has to go down as one of the best signings of last season.
Routledge ~£1.7M Not as good as the other 2 or even close, but he played 22 times in the league and did look decent on occasions
Gylfi Sigurdsson Loan - Not much needs to be said about him - 18 league apperances 7 goals 3 assits, up their with the best January signings.
He's has a couple of seemingly pointless signings like McEachran on loan or Bessone and a couple of not so impressive ones like Leroy Lita for £1.7 but that didn't exactly turn out to be diastorous as Swansea wern't short of goals. He's made a few average signings like Agustian and Luke Moore, but both helped out in the Promotion run and played some part in the impressive league finish
Reading FC will be seen as the blip on his current CV, his succesful transfer were:
Jodi McAnuff - 300k Their current Captian
Matt Mills: 2m Sold 2 seasons after for just over £5m
Ryan Bertrand- Ended up playing over 50 games for Reading (not all under Rodgers) and his development saw him start the Champions League final in May.
Can't find any information about his Watford signings he was only there for one transfer window, in January 2009.