Redwall by Brian Jaques.
The Belgariad and Mallorean by David Eddings. If you like those, there are also Belgarath The Sorcerer and Polgara The Sorceress in the same series.
Star Wars/Star Trek.
The David Eddings series is fantastic!! There are more too:
The Belgariad is Eddings' first fantasy series; The Malloreon is the sequel. The books follow the adventures of Belgarion, Polgara, Belgarath, and their companions.
The Belgariad series[edit]
1.Pawn of Prophecy (1982)
2.Queen of Sorcery (1982)
3.Magician's Gambit (1983)
4.Castle of Wizardry (1984)
5.Enchanters' End Game (1984)
The Malloreon series[edit]
1.Guardians of the West (1987)
2.King of the Murgos (1988)
3.Demon Lord of Karanda (1988)
4.Sorceress of Darshiva (1989)
5.The Seeress of Kell (1991)
Books related to The Belgariad and The Malloreon[edit]
Belgarath the Sorcerer (1995) with Leigh Eddings
Polgara the Sorceress (1997) with Leigh Eddings
The Rivan Codex (1998) with Leigh Eddings
The Elenium and The Tamuli
The Elenium and its sequel The Tamuli feature the Pandion Knight Sparhawk and his comrades.
The Elenium series[edit]
1.The Diamond Throne (1989)
2.The Ruby Knight (1990)
3.The Sapphire Rose (1991)
The Tamuli series[edit]
1.Domes of Fire (1992)
2.The Shining Ones (1993)
3.The Hidden City (1994)
The Dreamers series
The Dreamers series tells the story of a war between the Elder Gods and their allies and an entity known as the Vlagh.
1.The Elder Gods (2003) with Leigh Eddings
2.The Treasured One (2004) with Leigh Eddings
3.Crystal Gorge (2005) with Leigh Eddings
4.The Younger Gods (2006) with Leigh Eddings
(copied from Wikopedia) I have all of these and they are great. I have a daughter who is 9 and reads at an 11th grade level, it is hard to find series that are appropriate and yet complicated enough to hold her lol. She has read the entire Harry Potter series 4 times this year, I had to ban it for the rest of the year when she started phrasing everything Hogwarts style
The old S. E. Hinton books are still great reads- The Outsiders, Rumblefish, Tex, .. Hawks Harbor is also good but may not be suitable yet for that age.
I also agree with the Percy Jackson books, as well as the Artemis Fowl books by Eoin Colfer were great!
.. Sorry, avid book lover, married (formerly) to a book lover, family of book lovers, dream of a house with built in bookshelves in every room!!!
My middle son also loves sci-fi and I am trying to remember the name of the series he likes.