I loved the Weirdstone of Brasingamen and The Moon of Gomrath by Alan Garner.
The Narnia books by C S Lewis
The Silver Sword by Ian Serrailier.
I was given The Dangerous Book for boys about 4 years ago not fiction but worth getting.
Proffessor Brainstorm.
Stig of the Dump.
All great stuff but surely a bit younger than 11 or 12, I read most of those when I was about 8 to 10.