The Catalyst. Hated it when I heard it for the first time, then it slowly grew on me, and 2 years later I know every sound in it. Incredible stuff. Others would be New Divide, What I've Done, Numb, Breaking The Habit, Papercut, One Step Closer, ... the amount of awesomeness is ridiculous.
Don't Stay. Top-tier riff, the sound of the chorus is amazing, and it's overall one of my favorite songs of all time.