Here are two Blue Nile coupon codes (they call them reference codes) that I personally used successfully today:
VISAW29 to get 10% any purchase made with a Visa Credit Card. This expires October 31st, 2009.
MCARD08 got me 10% a Mastercard purchase. This one expires at the end of the year.
Just enter these in during checkout, in the box that calls for a “reference code”. There were a few more I found on the internet, but these are the ones that I actually used today. I saved 100+ bucks!