I thought it might be interesting to start a sort of 'Where are they now?' thread for wonderkids from older versions of FM/CM. I have only been playing since CM05 but I still have a few:
Anthony Vanden Borre: Was an excellent right-back playing for Anderlecht on the first CM games I played and also on FM07, tailed off a little after that. IRL he left Belgium for spells in Italy and England, and now plays in Ukraine for Tariya Simferopol, as well as making 23 appearances for his national side.
Slobodan Rajkovic: Serbian defender from my early days of playing Championship Manager. Moved to Chelsea IRL so there were suggestions he might fulfill his in-game potential. He never made an appearance there however he has amassed 13 caps for Serbia and currently plays in Germany for Hamburg.
Besian Idrizaj: A talented left winger in CMs from the mid-noughties. However his playing career was cut short when he died of a heart attack at the age of 22 as a Swansea City player.
Nicolás Millán: A prodigious talent both in FM and real life. He was an FM07 legend, and made his real-life debut for Colo Colo at just 14 and starring for the Chile U-17s. However, he never represented his country at a higher level or played for Colo Colo again, and is now on loan at Unión Temico.
Giorginio Wijnaldum:An FM wonderkid for years, is the only player on the list currently fulfilling his high potential. After successful spells with Feyenoord and PSV, the highly-rated playmaker now plays for AZ, and scored on his debut for the Netherlands in 2011, still aged just 20.
I have plenty more wonderkids to add in time. Feel free to share your wonderkids/memorable players!