Until I have time to properly investigate how the FIFA 11 manager mode works here is some raw player data extracted from the FIFA database. The potentials are to be used as a rough guide to player growth but may be some way off. Generally the younger players on this list are more likely to reach their potential than those 23+. These values were taken from the PC database but should also be accurate for finding the best players on xbox360 and ps3. As always, feel free to leave a comment if you find any awesome new players or good bargains.
There are a number of players included in FIFA 11 because they are part of their national team, but their club is not represented in the game. This means that in Manager Mode they will not be part of your. The following list of players are those that meet this criteria.
This post by Muzzy77 on the EA forums explains how you can add them to your game.