In a previous thread, several posters claimed that even if a woman chose to keep her name after marriage, the only "proper" way to address the couple in formal correspondence was still Mr and Mrs HisName. (@LDWed, CatsBoninCats, Ali)
The Internets and Emily Post have come to the rescue and I am pleased to tell you - that is NO LONGER TRUE. You can now acknowledge a woman's identity in addressing correspondence to a married couple without offending antiquated etiquette notions that only your grandma might actually care about!
http://emilypost.com/advice/guide-to-addressing-correspondence/
"Married, she uses maiden name:
Mr. John Kelly and Ms. Jane Johnson
Ms. Jane Johnson and Mr. John Kelly"
"To a married woman doctor or two married doctors:
If the woman uses her husband’s name socially, the address is “Dr. Barbara and Mr. James Werner.” If she uses her maiden name both professionally and socially, it is “Dr. Barbara Hanson and Mr. James Werner"