WordNet (r) 3.0 (2006):

prettify
    v 1: make more beautiful [syn: fancify, beautify,
         embellish, prettify] [ant: uglify]

Moby Thesaurus II by Grady Ward, 1.0:

56 Moby Thesaurus words for "prettify":
   adorn, array, beautify, become one, bedeck, bedizen, blazon, color,
   dandify, deck, deck out, decorate, dizen, doll up, dress, dress up,
   embellish, emblazon, embroider, enrich, extenuate, fig out, fix up,
   furbish, garnish, glamorize, gloss over, grace, gussy up, ornament,
   paint, prank, prank up, preen, pretty up, primp, primp up, prink,
   prink up, redecorate, redo, refurbish, set off, set out, smarten,
   smarten up, spruce up, sugarcoat, titivate, trick out, trick up,
   trim, varnish, veneer, whiten, whitewash