I was thinking if Zlatan Ibrahimovic was Inter's best transfer, at least in the last 20 years.
Sure, it's not the same case with Zidane and Kaka who were bought for less than 10m and then, after being the best players of Juve/Milan and after bringing trophies to their teams, they were sold for ~70m. The numbers aren't as high in Zlatan's situation, but still, the profit Inter made is remarkable.
They bought Zlatan from us [

] for ~25m eur (24.8).
After 3 scudetto winning seasons where he was their best player, after being their topscorer in all 3 seasons (66 goals total) and top assistman in 2 of the 3 seasons, they sell him for 46m eur+Eto'o+Hleb on loan.
Inter made ~21m eur cash profit and on top of it they got a great player like Eto'o and they also got Hleb on loan.
Watching this today, one can safely conclude that Zlatan was pure gold for Inter, no matter how you look at it.
But the future will give the final answer if Zlatan's transfer out of Inter was indeed a great piece of business.
Creating a winning team is very hard. Inter know this very well after 19 years of misery. When they finally created the winning team (one mustn't forget Calciopoli though as a factor in this), Zlatan was its main component.
When we sold Zidane and when Milan sold Kaka, Juve and Milan were coming after 2-3 trophyless seasons. Something simply had to be changed.
In Inter it's different. They already had the winning team and now it's one big question mark if they'll remain winners after selling their best player.