General Synonyms:
* Equitable
* Fair
* Equal
* Harmonious
* Proportional
* Symmetrical
* Stable
* Even
* Regular
* Moderate
Synonyms for specific contexts:
* Well-rounded (personality, education, etc.)
* Neutral (opinion)
* Even-keeled (emotionally)
* Controlled (diet)
* Stable (budget)
Antonyms:
* Unbalanced
* Uneven
* Imbalance
* Skewed
The best synonym for "balanced" will depend on the specific situation and the intended meaning.