Hi mm9 !
If you are looking for a good Central Defensive Midfielder then please give a try to Cameroon player MARC VIVIEN-FOE. He is a decent player with the most important stats (tackling, positoning, marking, heading strenght, stamina and determination above all) reaching 20 ( if not - he'll improve them).He is not the youngest of guys around yet he won't let you down. At the start of the game he plays for Lyon - French 1st division side, but he is willing to move to a other club.
I know that those 'visible' stats do not prove the player will perform well, but at least they indicate that he might be useful.
If, for some reason, he will decide not to join yor club you can try with following players( also central DM's):
Nicky Butt - ManU, obvoiusly
Assane N'Diaye - Shakhtar ( I also recommend a defender Isaak
Okoronkwo )
Radoslaw Kaluzny - Cottbus (German 1st Bundesliga)
Josep Guardiola - free transfer (quite old)
I have to say that Vieira is an awesome player, but there are many high-quality players ( DM C) around, so cheer up and search for them.
Personally, I concieve a central defensive midfielder as the most important figure in my tactics, so it is crucial for me to get a good player for this position. This is the reason why I've tested plenty of players and you can rely on those guys I've just mentioned. Still, I believe the best sollution is to search for players on your own. It's real fun!
Good luck.