I've already gotten him some of Feynman's books. He loves them. Weird kid won't read fiction, but loves Science books and manuals.
By the way, Molly, has your husband tried L-tyrosine? It's an amino acid that's good for sleep and depression. Seratonin is the precursor to L-tyrosine, which is the precursor to dopamine. Some folks have trouble converting from seratonin, so supplementing with tyrosine takes one step out of the process. I did notice a little improvement myself, but for sleep it was sporadic. Mood uplift was most of the time. The IMPORTANT thing to do when taking tyrosine is to not follow the bottle's directions. The bottle says to take before bed.
My doctor explained that there's only a finite number of amino acids the brain will allow past the blood-brain barrier, so they're competing to be the first to the brain. It's hard to ensure which gets there from just eating whatever food you want. The doctor said to take the tyrosine first thing in the morning, before you eat anything. That way, the tyrosine is the first to the brain, so is guaranteed to be among those the brain will use that day.