I remember when we were working on programming projects in college, we used to play the Jurassic Park theme (by John Williams).
It starts out really slow and steadily builds up. In my opinion it's great for getting motivated and to feel like you're doing something great ;-)
John Williams created lots of well-known movie themes (e.g. Superman, Indiana Jones, Star Wars, E.T., Jaws, etc.).
The Jurassic Park theme can be found on Youtube
. More on John Williams can be found on Wikipedia