Leviathan by Scott Westerfeld
Remember the show Wild Wild West. It was great, huh? And it could be called steampunk. I've found I really like this genre. Steampunk books take place in the past but have other aspects that are futuristic or science fiction. The Parasol Protectorate Series is steampunk. So is Leviathan, a science fiction/alternate history/steampunk novel for teens.
Leviathan takes place at the very start of The Great War (later to be known as World War I). Alek must hide his identity as he races from the Germans. He and his crewmates pilot a two-legged walking machine. (I pictured something similar to an AT-AT Walker from Star Wars: Return of the Jedi.)
Deryn must hide her identity as well. A girl would never be allowed to join the military, but she won't let that stop her from achieving her dream of serving on airship. The airship she ends up on is no ordinary airship. It's actually a whale who's life thread have been incorporated into a blimp like machine.
The Darwinists use life threads of animals to create useful devices. The Clankers rely on metal and machinery to do their work. We follow Alek, a Clanker, and Deryn known as Dillan, a Darwinist on their dangerous journeys filled with danger and suspense and a bit of humor. It's a great book! It might even inspire you to investigate a little more about WWI.
I knew there was a sequel, Behemoth, but I didn't realize Leviathan would end in the middle of the story, leaving us with a big cliff hanger. Luckily for us, Behemoth, is out, and the third book,Goliath, is due to come out September 20th!
[I listened to the audio book of Leviathan, which was very good, but I haven't seen the names in print. I think they are all spelled correctly except maybe Dillan.]