- Help Me Be Good series by Joy Berry. Its 28 books, each about a particular misbehavior: stealing, cheating, lying, etc. When I was a kid, if I ever did something bad, part of my punishment was that my parents would read the book about whatever I did wrong, and we reflect on why that was wrong and what I can do better. We'd also read them not as part of punishment, which always felt better since I wasn't in trouble for anything, but also helped solidify the values.
- DK makes great books for all ages, you can't really go wrong there. I always enjoyed the Illustrated Guide to World Myths. I'll probably buy some of the illustrated history books for my kids.
- My parents put a bunch of art books about famous artists on the shelf: Davinci, Michelangelo, Van Gogh, etc.
- Narnia series by C.S. Lewis. They also make a graphic novel of The Lion, the Witch and the Wardrobe.
- Dinotopia by James Gurney
There's a lot I'm leaving out but those are a good start. I'd also look for recs from mom-and-pop bookstores and your child's school if you are able.
You can also just go flip through a few dozen at the library. You don't have to buy all your books, and you can use the library to find decent ones you might want to have around all the time. Also, just ask the librarians, like, "what's a good children's book with dinosaurs?" or whatever. Or look out for the ones they're highlighting with placement.
[FURTHER EDIT] Here's a new parents starter pack I guess, why not:
1) Suess — Hop on Pop, The Sleep Book, Horton Hears a Who!, I Had Trouble in Getting to Solla Sollew, The Lorax, et c. They almost all read smoothly despite all the gibberish (reading clunkily aloud is a real problem with books—I've had "easy" children's books that were hard to read aloud and "hard" books that were actually pretty easy to read aloud, like Woolf's To the Lighthouse [you can read literally anything to kids who are too young to focus well on pictures, or if they're in the bath or otherwise unable to really look at the book anyway—I'm no specialist in child development but I'd assume just hearing language-noises is all they really need, then; three-for-three remarkably-early talkers with sky-high working vocabularies before 18 months, so, dunno if that helped, but it must not have hurt, though I suspect it's mostly luck/genetics])
2) Madeline. Classic for a reason.
3) Wild About Books (reads great, lots of fun visuals; I had this damn thing memorized at one point, didn't even need to look at the text)
4) Alice in Wonderland and The Jungle Book are good read-alouds that aren't picture books.
5) How the Sun Was Brought Back to the Sky — good entry in the "quest with repetitive steps and a character picked up each time" genre, which is a whole thing in picture books. See also Room on the Broom, which is also quite good and reads well. In fact, maybe prefer that one.
6) Lots of the early Golden Books that aren't licensed properties—The Little Engine that Could, et c.
7) Mike Mulligan and his Steam Shovel
8) The Velveteen Rabbit (beware—it'll make the room a tad dusty)
9) Mother Goose nursery rhymes, enough exposure that they won't miss references to them, at least (I suspect we're losing these as a cultural touchstone, but enough references hang around from past media that they're good to be familiar with—I'd wager what's replacing them and a bunch of other classics is Disney shit, which has overwhelmed kids' media and brain-space). Popular collections of these are readily available used, they're everywhere.
10) D'Aulaires' Norse and Greek Myths books. Read-aloud early on as they're not picture books (but they have pictures), later they can make good books for the kids to read themselves, if they're into this stuff.
There are dozens to hundreds of other good ones, but those are a decent start. You'll probably regret few or none of those purchases.