Going on FM standards, I think I deserve the title of "Best transfer ever" by selling Rory Fallon to Wolves for £1.2 million on FM06.
You're beginning to sound like Mike D
I had one once (can't remember what version of the game CM4/FM05) where I sold Freddy Adu to Spurs for £120m. In the January transfer window it turns out Spurs are mega skint (I wonder why) and are struggling in the relegation zone. So I purchased Freddy Adu back from them for a mere £9m. You've got to love the realism on these sorts of games