Out of the reported CB targets, I think Kompany would be the best option. Obviously not gonna happen though, unless he hands in a transfer request or something and then is willing to take a pay cut.
I think Vertonghen might be the best option (would have made a lot more sense to get him last summer, but oh well). Subotic might be a good one as well, though he hasn't really been linked with us. Hummels might be a good option, but I'm not sure how well Pique and him would work. Inigo Martinez is cheaper than the other options so he could be a good bargain. I do hope management go for the best option though, and not necessarily the cheapest.
As for Amorebieta, he might be a decent option for depth since he'll be free. We definitely shouldn't get him as a starter though.
Next summer the priority should be our defense...
We definitely need 2 proper CBs, one of them must be a real top class player and the second can be younger and preferably from La Liga...
We also need a backup LB, because Adriano is so injury prone and Abidal is still a question mark...
And finally we need a young GK if Valdés stays, or a top class GK if he leaves...
After all those spots are secured we can worry about who ever should reinforce our front line...
Montoya can play at LB. We may be able to get a CB who can play there as well (like Vertonghen). Don't think LB is too big an issue.
I don't think we need any new forwards. We do have the best attack in the world, after all. Villa's getting a little old, but he still has a good few seasons in him. We might want to look for his replacement next summer, but he'll definitely be good enough for next season. We have Tello and Deulofeu coming up as well.