Fantasy

Chaos Walking Series by Patrick Ness

The Knife of Never Letting Go, The Ask and The Answer, Monsters of Men
  
Predator Cities Series by Philip Reeve

Mortal Engines, Predator Gold, Infernal Devices, A Darkling Plain
  
Noughts and Crosses Series by Malorie Blackman

Noughts and Crosses, An Eye for an Eye, Knife Edge, Checkmate, Double Cross
 
Tunnels Series by Roderick Gordon and Brian Williams

Tunnels, Deeper, Freefall, Closer, Spiral, Terminal
 
Uglies Series by Scott Westerfeld

Uglies, Pretties, Specials, Extras

Hunger Games Series by Suzanne Collins

The Hunger Games, Catching Fire, Mockingjay

Gone Series by Michael Grant

Gone, Hunger, Lies, Plague, Fear, Light