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/