Hey there, here is my set up:
GK: Hart/Schmeichel
DC: Cáceres/Kompany
DL: Roberto Carlos/Gooré
DR: Jagielka/Zabaleta
DM: Veloso/Polombo
MC: Hamsik/Johnson
ML: Robinho/Petrov
MR: S.W.P/Arshavin
ST: Pandev/Jo
ST: Balotelli/Hulk
Veloso is great, fantastic stats and one of the best DM's in the game, and he actually wanted to come to Man City, although I can see you have Fernandes there.
As Leicester4Life said, Sakho and Fazio would be great additions to your squad, especially Fazio as DC.
As good as Roberto Carlos and Gooré are playing for me, they were only cheap transfers in the need to replace Garrido as he wanted to leave, so I would recommend
Hamsik was someone I bought as I needed a good MC to replace Johnson, as he is quite average, and despite Middlesbrough's countless bid's in January's transfer window, he would not accept their contracts! Although, I have yet to receive any good return from so far, but time will tell what he has to offer my squad.
Balotelli is someone I would class in high regard, has had a good return for me, he cost about 15mil I think and is certainly a wonderkid, and by that I mean a good one that you can actually play now, not wait 4 seasons for them to become reasonable.
You seem to be set for a right back, Richards is great (although I got a good deal for him from Barcelona so I sold up and bought a cheaper equivalent as the first half of my (first) season was quite poor, to improve in other areas.
What formation are you running?