The Collaborative International Dictionary of English v.0.48:

balanced \bal"anced\ adj.
   being in a state of proper balance or equilibrium; --
   opposite of unbalanced. the carefully balanced seesaw a
   properly balanced symphony orchestra a balanced assessment of
   intellectual and cultural history a balanced blend of
   whiskeys the educated man shows a balanced development of all
   his powers [Narrower terms: counterbalanced,
   counter-balanced, counterpoised; well-balanced; poised]
   [Related terms: stable --- (maintaining equilibrium)]
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

well-balanced
    adj 1: in an optimal state of balance or equilibrium; "a well-
           balanced wheel"
    2: free from psychological disorder; "a well-adjusted
       personality" [syn: well-adjusted, well-balanced]

Moby Thesaurus II by Grady Ward, 1.0:

63 Moby Thesaurus words for "well-balanced":
   assured, balanced, coequal, collected, commonsense, composed,
   confident, cool, coolheaded, coordinate, equal, equanimous,
   equilateral, equilibrious, eurythmic, even, fast, fiducial,
   finished, firm, firm as Gibraltar, harmonious, imperturbable,
   in equilibrium, levelheaded, logical, philosophical, poised,
   practical, pragmatic, predictable, proportioned, rational,
   reasonable, recollected, regular, reliable, sane, secure,
   self-assured, self-confident, self-controlled, self-possessed,
   self-restrained, sensible, sober, sober-minded, solid, sound,
   stable, steadfast, steady, substantial, symmetric, together,
   unflappable, unflinching, uniform, unshakable, unwavering,
   well-set, well-set-up, without nerves