Good Night Moon by Margaret Wise Brown. I also have this in Spanish for work and it's simple enough for me to read to Ben too.
Dr. Seuss' ABCs.
We read this aloud when I was pregnant with Ben and it still calms him when he hears it now.
I Am a Bunny by Ole Risom & Richard Scarry. My mom says this was her favorite book to read to Tony & me, and Dave and I love reading it to Ben. Simple, flowing text and typically great Richard Scarry illustrations that follow Nicholas the Bunny through the different seasons.
Hand, Hand, Fingers, Thumb by Al Perkins
We are on our second copy of this one (thanks, Uncle Tony!) because the first one got so loved/chewed up! Fun rhyming text.
Going On a Bear Hunt by Michael Rosen & Helen Oxenbury. Ben likes the action words and sometimes chimes in on the repeated "uh-oh!"
I See, also illustrated by Helen Oxenbury. A very simple book, this entertained Ben through many diaper changes when he was 6-12 mos. Ben loved saying "baby!" and pointing to the different objects introduced. We also borrowed I Hear, in the same series, from the library. Another delightful book by Oxenbury and Mem Fox is Ten Little Fingers and Ten Little Toes.
Is Your Mama a Llama? by Deborah Guarino. Memorizing this book and being able to recite it to Ben while driving has staved off many a road trip meltdown! It is now one of my favorite children's books; nice but not overly-cutesy drawings and clever rhyming text.
That's Not My Dinosaur! by Fiona Watt and other That's Not My _____ books. We have a great video of Aunt Mary reading this to Ben on our trip to South Carolina last fall.
Good Night, Gorilla by Peggy Rathmann. We had to take this out of Ben's bedtime book choices because he wanted it read over and over again. He melted down one night because we wouldn't read it a sixth time. Now it's a daytime book. He will also sit and flip through the pages by himself for several minutes at a time. Simple text but detailed illustrations that encourage the reader or child to add their own observations and details.
There are so many more he likes, but those are some of his top choices to read repeatedly. What are your favorite books for young children?