The Collaborative International Dictionary of English v.0.48:

Natty \Nat"ty\, a. [Cf. Neat clean.]
   Neatly dressed; smart; trim; tidy; spruce. [Colloq.]
   [1913 Webster] -- Nat"ti*ly, adv. -- Nat"ti*ness, n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

natty
    adj 1: marked by up-to-dateness in dress and manners; "a dapper
           young man"; "a jaunty red hat" [syn: dapper, dashing,
           jaunty, natty, raffish, rakish, spiffy,
           snappy, spruce]

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "natty":
   bandbox, braw, chic, classy, clothes-conscious, cosmopolitan,
   dapper, dashing, doggy, dressed to advantage, dressed to kill,
   elegant, exquisite, genteel, jaunty, neat, nifty, nobby, posh,
   recherche, ritzy, sassy, sharp, sleek, smart, smug, snazzy, soigne,
   soignee, sophisticated, spiffy, spruce, style-conscious, swank,
   swanky, swell, tricksy, trig, trim, well-dressed, well-groomed