There are a variety of drugs that can help. Try new things in your sex life, and ask you husband if there was anything sexually he's always wanted to try. Explore new things, and maybe that could help spark his interest in sex.
Don't use any herbal remedies, though. They cause a lot of problems.
Did he try drugs like Viagra or Enzyte?
What a lucky woman you are that you have a husband that is willing to work with you to find a solution to this problem. Most women would kill just to have their husbands go to the doctor to be checked. CurleyGirl is right, there are several medications out there that can help in that area, and if he is willing to try them, you will not be dissappointed. In reality men are no different then women as far as our bodies go, things change in them the way hormones change in us. Women however are just programmed to see a doctor when they have changes where men are not. So, keep your chin up and don't give up until you reach a conclusion that satisfys both of you.