WordNet (r) 3.0 (2006):

suspenseful
    adj 1: (of a situation) characterized by or causing suspense
           [syn: cliff-hanging, suspenseful, suspensive,
           nail-biting]

Moby Thesaurus II by Grady Ward, 1.0:

92 Moby Thesaurus words for "suspenseful":
   agitated, agitating, all-overish, anxious, anxioused up,
   apprehensive, at issue, bothered, breathtaking, charged,
   cliff-hanging, concerned, conditional, conditioned, contingent,
   dependent, depending, disquieted, disquieting, distracting,
   disturbed, disturbing, electric, exciting, exhilarating, fearful,
   foreboding, galvanic, heady, heart-expanding, heart-stirring,
   heart-swelling, heart-thrilling, impressive, in a pucker,
   in a stew, in question, in suspense, in the balance, inflammatory,
   intoxicating, jarring, jolting, maddening, mind-blowing, misgiving,
   moving, nervous, on tenterhooks, open, overanxious,
   overapprehensive, overcoming, overmastering, overpowering,
   overwhelming, pendent, pending, perturbed, perturbing, piquant,
   provocative, provoking, ravishing, solicitous, soul-stirring,
   spirit-stirring, stimulating, stimulative, stirring, strained,
   striking, suspensive, tantalizing, telling, tense, thrilling,
   thrilly, troubled, troubling, uncounted, undecided, undetermined,
   uneasy, unestablished, unfixed, unsettled, unsettling, untold,
   up for grabs, upsetting, zealous