Hang premade posters of physics cartoons or of Einstein making his signature funny face, alongside typical physics charts and graphs, to liven up your walls.
Instruct students to make posters as an assignment. Make it into a contest among the students. The student who designs the best physics-themed poster not only gets his poster displayed on the classroom wall, but also wins a prize, scores extra credit or whatever other incentive you wish.
Display other projects and assignments the students completed around the room. Optionally, add ribbons marking first, second and third place to exceptional pieces of work.
Throw up a few pictures or place a couple other items around the room that have personal meaning to you or the students. Whether they apply to a lesson or not, they can add character to your classroom.
Take your class outside, if permitted by your school administration, for an entire lesson. Physics is all around us. Prove that to your students by showing them everyday examples of physics in the "real world."
Take your class on field trips to get the kids excited about the subject. If an off-site field trip isn't possible, take them around the school. Ask other teachers to allow you to visit their classrooms, including the gym or theater area, if applicable.
Rearrange the desks without notifying the students. Arrange them into a circle or into two groups facing each other. This may be distracting at first, but can create a different classroom dynamic. Change the seating arrangement whenever possible to rekindle that excited spark in your students. Request help from the janitorial staff or other teachers, if needed.
Move your desk, as well, to different areas of the classroom. If you utilize a blackboard, whiteboard or smart board, work around that. The new arrangement will energize you, too, making the class more fun for you and your kids.