Scott Westerfeld, who wrote 'Leviathan', has a whole catalog beyond that fantastic series. His 'Uglies' trilogy (and the extra book 'Extras') was huge for me as a teen—it’s a sharp dystopia about a world where everyone gets mandatory cosmetic surgery at sixteen. It hit a different nerve than the steampunk of 'Leviathan', more about social pressure than clanking machines, but that same punchy, imaginative world-building is there.
He also did the 'Midnighters' series, which is this cool premise about a secret 25th hour of the day only a few teenagers can access, and they have to fight ancient creatures. It’s weirder, darker YA. Then there’s 'The Risen Empire' duology, which is adult space opera, really polished and epic. His range is underrated. I keep hoping he’ll circle back to more in the 'Leviathan' universe someday, but I’ll take anything he writes.