The Old Kingdom books (the Sabriel series) by Garth Nix. Some of my favorite books of all time, and should be right up your alley if you liked the Hobbit and a Wrinkle in Time.
In the same vein is the His Dark Materials series by Philip Pullman starting with the Golden Compass (Northern Lights in the UK I believe), another of my favorite books ever.
Brian Jacques' Redwall's also a timeless classic, though it's aimed a bit younger than the books you listed I think. Richard Adams' Watership Down is also excellent.
I'll add more if I think of any.
The Chronicles of Narnia are excellent, and hilarious, though they do get a bit religious.
Ender's Game is fantastic, though you may want to check this one out from a library instead of buying it to avoid supporting the author.