I have discovered that one of the best motivators in the classroom, for anything really, is getting students to like the teacher.
Once I had a good reputation at my school--not for easiness or even niceness--once students started to really like me, they seemed more motivated to do almost anything.
Building a personal repoire with your students is one of the best things you can spend time on as a teacher. Think about your favorite teachers of all time. Wouldn't you have pretty much done your best on anything for them?