The Collaborative International Dictionary of English v.0.48:

Uncomplaining \Uncomplaining\
   See complaining.

WordNet (r) 3.0 (2006):

uncomplaining
    adj 1: not complaining; "uncomplaining courage" [ant:
           complaining(a), complaintive]

Moby Thesaurus II by Grady Ward, 1.0:

48 Moby Thesaurus words for "uncomplaining":
   abject, accepting, accommodating, acquiescent, adapting, adaptive,
   adjusting, agreeable, amenable, assenting, at ease, comfortable,
   complaisant, compliable, compliant, complying, composed,
   consenting, content, contented, easy, easygoing, eupeptic,
   euphoric, happy, humble, meek, nondissenting, nonresistant,
   nonresisting, nonresistive, obedient, of good comfort, passive,
   pleased, reconciled, resigned, sans souci, satisfied, servile,
   submissive, subservient, supine, unassertive, unrepining,
   unresistant, unresisting, without care