Wow, so many of my favourites have already been mentioned - Enid Blyton (esp. the Five Find-Outers and Buster the dog - Mr. Goon was a great character!), Roald Dahl, Little Women, the 'Anne' books, any fairy tales (Hans Christian Anderson was a favourite), The Secret Garden, The Hobbit and the Lord of the Rings.
I don't think anyone has mentioned E.Nesbit yet - has anyone read 'Five Children and It' or 'The Phoeix and the Carpet'? Another favourite was 'The Lion, the Witch and the Wardrobe' by C.S. Lewis; I always regret that I didn't read the entire Narnia series until much later.
In my early teens I also enjoyed Piers Anthony's 'Xanth' series - very light, fun fantasy that seems to draw an immense amout of critisism! Is anyone else familier with this series?