I Don't Know What to Read

Newbery Medal Winners

http://www.ala.org/alsc/awardsgrants/bookmedia/newberymedal/newberyhonors/newberymedal

A Book and a Hug

https://abookandahug.com/

Goodreads

Highly searchable and lots of lists! Here are popular titles by grade level:

5th Grade

4th Grade

3rd Grade

2nd Grade

1st Grade

TK/Kinder

https://www.goodreads.com/

California Department of Education Recommended Literature List

A searchable collection of outstanding literature for children and adolescents in grades pre-kindergarten through grade twelve, in all disciplines.

http://www.cde.ca.gov/ci/cr/rl/