Appropriate Gift Giving ?

In my business dealings, I have often given a gift to someone I do business with. I have never included the CEO of the company or a spouse of my client unless I have also been, personally, doing business with them as well. Be professional, not invasive of your client's personal life. Do not treat this woman as a "wife" or "female". Treat her as a valued business professional. 

To gift a person, who is a client, has all the hallmarks of bribery.  Someone gains a personal kickback for their decisions on the part of the company.  Yes I know "bribery works" but it plunges us all into a third world country.  Keep it professional, not personal.

Your husband is correct.  Your business relationship with this client begins and ends with the point person (the wife).  If a gift is offered, it should be to her and her alone.  To gift both spouses would take away from the gratitude specifically meant for her, not someone you have never met.

Give her/them a gift card to a restaurant, or something they would both enjoy.

Only contact is with her, therefore she is the 

client, and therefore the gift should be for her. 

However, there is nothing wrong with making 

it something "generic" that they both can use 

(or she could more easily "re-gift" to someone 

if not needing/wanting whatever you gave her).

Gift to them both.. and a very nice dinner reservation, with all the bells and whistles would be my suggestion.  That way they both can enjoy the meal.

If she is the only one you have contract with then give the gift to her. There is no reason to give a gift to her husband. You have not met him nor are you in contact with him. 

Give a nice impersonal gift to her.

Order a basket from Harry and David.