IMO, what makes a good coffee table book is something that's appealing/accessible enough that it's going to get picked up and used to kick off a conversation. It can be about anything - it's the engagement that's important.

I think photography books are solid, and I have done a few in the past. But I get better results from "weird" stuff. Right now, I leave out my annotated copy of the Voynich Manuscript which is just so bizarre and fun to look at that people can't help themselves. I used to leave out a scrapbook that some dude put together in the 1880's. He made it from a conveniently coffee-table-book-sized lock & hardware catalog. It's like 200 pages of newspaper clippings from across the country, with a preface about the guy (who I gathered was a disabled eccentric) and why he put it together (which is far from clear). It was by far my best coffee table book because 19th century papers were BUCK WILD, but I ultimately retired it due to its condition.

I also mentioned elsewhere in the thread that I've accidentally left out some D&D books before, and people will flip through those pretty reliably.