Liber Mortis was the 3E undead book (expanding on 2E's Lords of Darkness and the Van Richten's monster hunter series), Lords of Madness covered aberrations (which was compiled from the I, Tyrant and Illithiad and expanded to cover Aboleths and others). They're still relevant for the lore portions - a lot of which made its way (though abbreviated) into the 5E monster entries. 2E's (FR) Giantcraft covered giants, I don't remember it being revised or updated for 3E forward. I don't remember a Fey book - that'd be a good one with all the focus of late on the Feywild, and dragons have had a book since the days of 2E/BECMI (Draconomicon/Book of Giants and Dragons). And there's also the Fiendish Codexes from 3E, which went in-depth into Demons and Devils, respectively. Again, a lot of that lore crept in, in abbreviated form, into the 5E monster entries.
That's why I'm not so interested in the lore books (except maybe one on Fey) - 2E or 3E did a lot of in-depth delving into monster lore, and short of a few stat blocks, it's all still relevant to the game today. I'm sure folks who don't have the old books would probably enjoy reprints/compilations/updated stats, but for me, I've still got those old books and wouldn't put out the money for them - for example, I'll take the 3E Draconomicon over Fizban's any day of the week if it weren't for the 5E Draconian stat blocks.