By now you should have a few people that would speak positively on your behalf if a potential employer came calling. It's even better if you can provide a mix of references. Instead of supplying only a list of your superiors, it adds depth to your character and work ethic check when you name at least one colleague.
Be choosy about the colleagues you include — you need to be confident in their ability to speak intelligently and they must have had substantial interaction with you in a work atmosphere, not just at happy hour. And remember the golden rule of references: always ask them if they're willing to be a reference before handing out their contact information.