I used to work at the Franklin Institute, so my recommendations are based on that.
I'd like to say that while I love the American Museum of Natural History in New York, it doesn't have the same kind of interactivity.
The Exploratorium in San Francisco does, although I don't remember it being as large at the Franklin Institute. It did have some very cool unique exhibits I hadn't seen elsewhere.
I quite liked the Boston Museum of Science - very similar to the Franklin Institute in many ways, so your husband may like it a lot.
The Liberty Science Center in New Jersey was opened by ex-Franklin Instituters, I believe, but the last time I went (admittedly, something like nine years ago), many of the exhibits were in terrible disrepair.