Harry Potter by J.K.Rowling
HP & the Sorcerer's Stone
HP & the Chamber of Secrets
HP & the Prisoner of Azkaban
HP & the Goblet of Fire
HP & the Order of the Phoenex
HP & the Half-Blood Prince

Merlin epic by T.A.Barron
Lost Years of Merlin
Seven Songs of Merlin
Fires of Merlin
Mirror of Merlin
Wings of Merlin

If you like Harry Potter and wizard stories, try these:
The Bartimaeus Trilogy: Amulet of Samarkand, Golem's Eye, Ptolemy's Gate
The Earthsea series: Wizard of Earthsea, Tombs of Atuan, Farthest Shore

Redwall series by Brian Jacques
Author recommends reading books in publication order.

Publication order:
Redwall
Mossflower
Mattimeo
Mariel of Redwall
Salamandastron
Martin the Warrior
The Bellmaker
Outcast of Redwall
Pearls of Lutra
Long Patrol
Marlfox
Legend of Luke
Lord Brocktree

Redwall series by Brian Jacques

Story Chronology:
Lord Brocktree
Martin the Warrior
Mossflower
Legend of Luke
Outcast of Redwall
Mariel of Redwall
The Bellmaker
Salamandastron
Redwall
Mattimeo
Pearls of Lutra
Long Patrol
Marlfox

A Series of Unfortunate Events by Lemony Snicket
The Bad Beginning
The Reptile Room
The Wide Window
The Miserable Mill
The Austere Academy
The Ersatz Elevator
The Vile Village
The Hostile Hospital
The Carnivorous Carnival
The Slippery Slope
The Grim Grotto
The Penultimate Peril
The End

Dark is Rising by Susan Cooper
Over Sea, Under Stone
The Dark is Rising
Greenwitch
The Grey King
Silver on the Tree

For more info on series books, try these links:

Series & Sequels
YA Series & Sequels
Books In a Series