The people that I have worked for or with in the recent past.
I do not include my professional references on my one-page resume or even on my expanded resume.
I wait until the Employer or Interviewer asks for my references.
I believe that my references are my post important asset in my job search process.
I know that wherever I have worked - I have been very diligent and performed to the best of my abilities. My former employers can all speak candidly and truthfully about my work - and they can all give me a good recommendation.
But - their time is valuable and I respect them very much. I do not want everyone that receives one of my resumes to call them and interrupt their work. They will be happy to speak with serious seekers, but they should not be bothered by anyone who is still trying to figure me out.
I have their permission to submit them as References, and I have their contact information. They are expecting a call or a contact.
For a Tech Resume I only send two or three references.
They are Professional References, not personal.