The 3e Eberron books are numerous, but not all of the same quality. The further they get away from the original design team the more they suffer. Anything with Keith Baker or James Wyatt on the cover is probably at least decent, but that's not everything.
The three books I made sure to keep were the Eberron Campaign Setting, Sharn: City of Towers, and the Player's Guide to Eberron. You might get some decent millage out of Secrets of Sarlona and Secrets of Xen'drik. But I would probably avoid, say, Five Nations or Magic of Eberron. I recall those as being noticeably lower quality.
If you want a shorter shopping list, the 5e Eberron: Rising from the Last War is decently concise and has some useful updates. Also Keith Baker put out a book through DMs Guild, Exploring Eberron, that I found an excellent deep dive into some of the aspects of the setting that don't usually get a close look.