Nasri.
Don't really understand the need for Isco anyway. He plays better when he's central. He's less effective when on the left. We bought Nasri off the back of him having a brilliant season for Arsenal where he predominantly played in he centre due to the absence of Fabregas. We bought him and deployed him on the left where he lacks the acceleration and directness to create goal scoring opportunities.
Isco looks a great player, but an on form Nasri alongside Silva is already brilliant. Then you still have to find positions for Aguero, Navas, Tevez and Dzeko.
More than anything we need a right sided centre half who is capable of performing at a similar level to Kompany and Nastasic for 20 games a season. And we need to keep Lescott purely because Nastasic may need a break at some point next season. Young players tend to go off the boil for a while after playing in the first team. Micah Richards had a similar problem when he was in his teens.
Other than that, depending on who leaves, we need replacements, not signing for positions where we are already strong.