If You  Liked Holes by Louis Sacar, You Might Also Like:

Alexander, Lloyd. The Prydain series.

Bloor, Edward.  TANGERINE.

Carter, Peter. Borderlands.

Cooper, Susan.  THE DARK IS RISING (series).

Duane, Diane. The Wizardry series.

Goldman, William. The Princess Bride.

Howe, Norma.  Adventures of Blue Avenger. 

Ibbotson, Eva. The Secret of Platform 13.

Jacques, Brian.  REDWALL (and others in the series).

Jones, Diana Wynne. Series: The Crestomanci Novels and the Dalemark.

Jones, Diana Wynne. Howl’s Moving Castle.

Eldest of three sisters in a land where it is considered to be a misfortune, Sophie is resigned to her fate as a hat shop apprentice until a witch turns her into an old woman and she finds herself in the castle of the greatly feared wizard Howl.

L’Engle, Madeleine.  A Wrinkle in Time.

Levine, Gail Carson. Ella Enchanted.

Lewis, C.S.  THE CHRONICLES OF NARNIA (series).

Lynch, Chris. Slot Machine.

McKinley, Robin.  The Hero and the Crown.

Paulsen, Gary. Harris and Me: A Summer Remembered.

Sent to live with relatives because of his unhappy home life, a young boy meets his cousin Harris and is introduced to a whole new world.  

Pullman, Philip.  His Dark Materials (series).

Much darker than Harry Potter, and more difficult reading, too, but well-written.

Sheffield, Charles.  Putting Up Roots.

Same idea,  on  another planet, disenfranchised kids, digging holes for the bad guys...

Smith, Sherwood. The Wren Trilogy:  Wren to the Rescue; Wren's Quest; Wren's War

These are about an orphan who finds out she has magical powers.  Her best friend turns out to be a princess and the two--in the first book--return to the princess's home where Wren will learn how to use her powers.  The princess is kidnapped and Wren rescues her.  The last book is the darkest, as the princess's parents are killed and she must raise an army to retake her kingdom, with the help of Wren and friends. 

 Wrede, Patricia.  The Enchanted Forest Chronicles (series).   

Yolen, Jane.  Wizard’s Hall.