Javi. Martinez.
Him and Alba are all we need, with them and an in-form and well rested David Villa along with the momentum we will have after half of our starting XI has won the Euro (interesting fact: everytime Spain has won a major international tournament, Barca have gone on to win the Champions League the following season), I see us taking back Spain and Europe in emphatic fashion. With Javi Martinez, we get a player who can play as both a DM and a CB, he is tall yet he is not a mere copy of Pique (like Hummels, and like others have said, we need a player who complements Pique yet isn't too similar). With him and Alba, our defense would be a lot deeper and we could save Puyol for the big games while Masche and Martinez take the leftovers (which will be quite a few).
I would be happy personally if those were our only buys this summer bc we don't need to change a lot. We are still head and shoulders above every other team in Europe, the only way teams are able to get by us is if they park the bus and hope they get a scrappy, lucky goal.
The only other players I would like to see us buy are young kids. I would buy back Romeu from Chelsea since we lost Keita, he has a bright future and if we give him some playing time, he could be another player for our future midfield, like Thiago. The other young kid I wouldn't mind seeing is Nelson Oliveria. I was pleasantly surprised with the skills he showed in the Euro whenever he got a little playing time, and I think he has a lot of potential. I would rather us get him than Adrian, since he will be cheaper and not be expecting to play a lot.