The old-fashioned nursing whites would be great, but the newer green (or blue) scrubs do nothing for me. Personally, I love to see a woman in a suit (business or formal), or dressed up like a $1000 a night prostitute, though I suppose neither of those could really be considered a costume.

I have a recurring image in my head of a woman in a tuxedo top and tophat, and open-weave stockings and high heels below. She's walking up and down on top of a long bar (as in fountain drinks) in a smoke-filled night club, playing a slide trombone... Ack! Too much information!