For most of the Alabasta arc Nami wears a blue dancer girl's outfit, and on her feet she wears the same tan sandals she wore back in Cocoyashi Village.
This arc is notable in that Nami acquires the Climate Baton, which allows her to controls air properties and makes her into a more effective fighter. She uses the new weapon to defeat Miss Doublefinger.
Part 1: http://animefeet.blogspot.com/2014/05/one-piece-nami-arlong-park-arc.html
Part 2: http://animefeet.blogspot.com/2014/10/one-piece-nami-grand-line-arc.html
Part 3: http://animefeet.blogspot.com/2015/03/one-piece-nami-little-gardendrum-island.html