The Shawshank Redemption (1994, Tim Robbins, Morgan Freeman)

Briefly features a prison bus.
At the end of the movie, Red heads out of Maine en route to Fort Hancock in Texas on a Trailways bus number CSS-476 (thanks Geoff Cook). This was a Blue Ridge Trailways GMC PD-4104 restored as a Carolina Scenic Trailways bus. The driver was Bob Bryson. The tinted windows were replaced for the film with clear glass and reinstated afterwards. (from correspondence on Yahoo groups)
Also barely seen is a green and cream transit bus - fleet number may be 4109.