WordNet (r) 3.0 (2006):

posh
    adj 1: elegant and fashionable; "classy clothes"; "a classy
           dame"; "a posh restaurant"; "a swish pastry shop on the
           Rue du Bac"- Julia Child [syn: classy, posh, swish]

Moby Thesaurus II by Grady Ward, 1.0:

81 Moby Thesaurus words for "posh":
   Babylonian, Corinthian, a la mode, awe-inspiring, awful, barbaric,
   braw, chic, classy, clothes-conscious, cosmopolitan, dapper,
   dashing, deluxe, dressed to advantage, dressed to kill, elaborate,
   elegant, exclusive, exquisite, extravagant, fancy, fashionable,
   fine, genteel, glorious, grand, grandiose, imposing, impressive,
   jaunty, lavish, luxurious, luxury, magnificent, majestic, modish,
   natty, neat, nifty, nobby, noble, opulent, palatial, plush,
   princely, proud, recherche, regal, rich, ritzy, royal, sharp,
   sleek, smart, smug, snazzy, soigne, soignee, sophisticated, spiffy,
   splendacious, splendid, splendiferous, spruce, stately,
   style-conscious, sumptuous, superb, superfancy, superfine, swank,
   swanky, swell, tony, trendy, tricksy, trig, trim, well-dressed,
   well-groomed