WordNet (r) 3.0 (2006):

piece de resistance
    n 1: the outstanding item (the prize piece or main exhibit) in a
         collection [syn: collector's item, showpiece, piece de
         resistance]
    2: the most important dish of a meal

Moby Thesaurus II by Grady Ward, 1.0:

38 Moby Thesaurus words for "piece de resistance":
   boil, broil, casserole, champion, choice, chosen, course, cover,
   cream, culinary masterpiece, culinary preparation, dish, elect,
   elite, entree, fat, flower, fry, grill, main dish, masterpiece,
   nonesuch, nonpareil, optimum, paragon, pick, prime, prize, queen,
   quintessence, roast, select, side dish, superlative, the best,
   the best ever, the tops, the very best