Don't be afraid to ask the right people for references. The right people are your former bosses.
Tell your references:
1. I'd like you to be a reference in my job search.
2. Why you're asking them to be a reference. "I remember what a great boss you were," or "I learned a lot from you." Tell them something positive about why you want them as a reference.
3. Let them know you will not throw their name around lightly and that you will not be a burden to them.
Follow up by sending your resume and a note about what you're looking for, the companies you're targeting, and that you'll let them know when you have an opportunity you're interested in.
If you've interviewed and your references will be checked, alert them. Tell your references the position you're interested in, a couple items you learned about during the interview that are critical to the position, and how your skills meet those needs.
Most importantly be sure to say thank you.
Prep them appropriately and your references will be a positive asset when a potential employer calls.