Pretty broad request, here... are you looking for a specific mood or theme, or a certain writing style, or more modern verses older classics, or... ?
Some recs off the top of the head:
The Alexander Cold trilogy (first book: City of the Beasts), by Isabel Allende: Fantasy in the modern world, where an American teen boy discovers hidden, mystical wonders and abilities in the far corners of the earth.
Graceling, by Kristen Cashore: A fantasy world where odd-eyed people display unique traits, from useless (holding breath for a long time) to potentially devastating (always being believed when speaking, or an unnatural talent for killing.) Katsa, one of these Gracelings, has been used by her cruel uncle for years as an enforcer thanks to her devastating martial skills... but she hates what he makes her do, and finds ways to subvert his orders. Great if you want a strong woman MC.
The Artemis Fowl series (first book: Artemis Fowl), by Eoin Colfer: A clever update on fairy lore pits Artemis Fowl, a boy criminal mastermind, against the underground Fairy nation, which not only has magic but technology centuries ahead of our own. Good if you want to study how to blend humor with a compelling story.
These might lean more toward MG than YA, but I'll also recommend Rick Riordan's Percy Jackson series (first book: The Lightning Thief - a modern boy learns his absent father is a Greek god when monsters out of myth start attacking him), J. K. Rowling's Harry Potter series (first book: Harry Potter and the Sorcerer's Stone/Philosopher's stone, US/UK titles - an orphaned son of wizards discovers his birthright when he receives an invitation to a magical school), and Jonathan Stroud's Bartimaeus books (first book: The Amulet of Samarkand - an alternate-modern world is ruled by magicians, who get their absolute power by enslaving spirits).
If you're bored, hit the link in my signature for my reviews for more; I try to keep the first parts neutral, so just read the Descriptions if you only want an idea of what the book's about, not a review.