I love that second Lilly style!
We have to wear navy blue dresses for our philanthropy round, mine is from J. Crew. If you check out the bridal/bridesmaid section, they have some promotion running now for 30% off. It's expensive, but I'm actually wearing mine to a wedding over winter break as well!
http://www.jcrew.com/wedding/Wedding_Bridesmaid.jsp
And I know not everyone likes eBay, but it has been my SAVIOR for recruitment attire. I've gotten some J.Crew, Lilly, all NWT for a nice discount.
ASOS also has tons of navy options:
http://us.asos.com/women/