Yeah, actually the Psionic classes are a great example of class balance, as long as you:
1) ban a handful of specific Powers that are broken
2) ignore that the Psion is just as overpowered as other full casters like the Sorcerer, Favored Soul, etc. (but not as bad as Wizard/Cleric/Druid)
3) ignore the Soulknife ... completely.
That still leaves you with 5 psionic base classes that are pretty well-balanced. (I guess the Ardent is still a bit on the strong side.)