The books I'm going to list are ones I've read. They are all Newberry medal award winners for either best childrens' book of the year or runner up. Cynthia Voigt is an incredible young adult author, Madeleine L'Engle is phenomenal, and Paula Fox has written some great stuff too.
Lily's Crossing by Patricia Reilly Giff
Catherine, Called Birdy by Karen Cushman
The Whipping Boy by Sid Fleischman
Sarah, Plain and Tall by Patricia MacLachlan
One-Eyed Cat by Paula Fox
Dicey's Song by Cynthia Voigt
A Solitary Blue by Cynthia Voigt
Jacob Have I Loved by Katherine Paterson
A Ring of Endless Light by Madeleine L'Engle
The Westing Game by Ellen Rankin
The Slave Dancer by Paula Fox
From the Mixed-Up Files of Mrs. Basil E. Frankweiler by E. L. Konigsburg
A Wrinkle in Time by Madeleine L'Engle
The Wheel on the School by Meindert DeJong (my own personal favorite)
King of the Wind by Marguerite Henry
Misty of Chincoteague by Marguerite Henry
These Happy Golden Years by Laura Ingalls Wilder
Roller Skates by Ruth Sawyer