My 11 year old daughter is an avid reader of the Harry Potter books, but she's now read them all at least 5 times and would like to read other similar books, not necessarily about wizards etc. but with the same level of excitement in the stories.
Hi, try Philip Pullman; The Amber Spyglass, The Subtle Knife and Northern Lights.....an excellent trilogy. Or Sabriel, I think the author is Garth Nix.
How about The Hounds of the Morrigan by Pat O'Shea, or another Garth Nix series The Keys to the Kingdom - Mister Monday, Grim Tuesday, Drowned Wednesday, Sir Thursday and Lady Friday, with Saturday and Sunday still to come. Older but still good reading, The Weirdstone of Brisingamen by Alan Garner. The sequel, The Moon of Gomrath, wasn't as good in my opinion, but is still a good read
William Nicholson's Wind on Fire trilogy, which includes The Wind Singer, Slaves of the Mastery, and Firesong, or the Noble Warriors trilogy, by the same author, including Seeker, Jango, and Noman, another good trilogy is the Twilight series by Stephenie Meyer, the titles names being Twilight, New Moon, and Eclipse
Does it matter whether 'lajohn' is male or female? What was wrong with the Famous Five or the Secret Seven? I'm with Sir Alec on this one - The Chronicles of Narnia were/are great, ignore the recent films - imagination wins hands down! At 11 years old my local library was almost a second home, I read everything I could get my hands on, I developed a very fertile imagination as a result, it's a shame more kids don't turn their backs on television and transport themselves to another world through good, quality fiction.
The Book of Dead Days by Marcus Sedgwick was a hit with my niece. Not really wizardy, but has a sort of sorcerer/inventor, an underground alternative reality hidden city and a dark secret. Ticks all the boxes. I loved it too!
Forget all of the above (just kidding) and introduce Diana Wynne Jones into your lives. She is just unbelievably clever, funny and intricate. One particular set of her books deals with a character that is a gifted wizard, unknowingly. She's built an whole alternate set of worlds where magic is the main source of energy, opposed to electricity as in our world. Our world is just one of the many in this series of worlds, and the characters cross over them on occasion which comes as a shock when you see our mechanical age being viewed through the eyes of an outsider. The stories are really well plotted as well as being complex enough to engage you. They are also witty as hell. Please go to her website, it'll give you the whole list. http://www.leemac.freeserve.co.uk/
I'm thirty five, have been reading her books since I was about twelve and still look forward to new ones that I've not previously discovered.
Tanith Lee is another good author.