I actually stopped a bit as my current reading is "the bigger the better".
What about the classics like 20000 Leagues Under The Sea, H G Well's The War of the Worlds (science fiction,), The Neverending Story, The Lost World etc
Classics have the advantage of being cheap and short.
Also, I have never tried these stories yet but have the impression that they are good YA series :
Susan Cooper's The Dark is Rising
CS Lewis's Narnia
Lemony Snicket's A Series of Unfortunate Events
If you can post a few of your favourites, ppl can help you more.