Yellowstone is my favorite park, I'm so happy you are going for a visit and your husband will be working there.
Tell him to get used to being asked why are the little orange dogs following the buffalo
There are several books I've bought at Yellowstone that you can buy online, or maybe even find in a library.
I have volumes 1 &2 of The Yellowstone Story.
Roadside History of Yellowstone Park
Yellowstone Place Names and Death in Yellowstone by Lee Whittlesey,
who was the park historian last time I was there.
The last two are the most interesting.
I agree with another poster who said Lamar Valley was very nice.
In the evening there are usually people pulled of the road to listen to the wolves. Once you hear them, you'll never forget it
This is the website for the Yellowstone Association...
http://www.yellowstoneassociation.org/