Before you provide references to us, or any future employer, you need to check to make sure that each is ready, willing and able to serve as a reference. Double check contact information and provide multiple phone numbers. Have each person check their own Human Resources policy on what he or she is able to disclose. Is it simply employment dates? Fine. But we'll need some character references as well.
When conducting reference checks, I find it helpful to talk to folks who know our candidates from different angles; managers, peers and subordinates. Need to dig deeper? Think about people with whom you've served on committees for PTA, church or sports leagues.
The bottom line is that you want to make yourself EASY to hire. If a hiring manager has to leave several messages for reference checks, if a number is no longer in service or if a reference can't provide any good information, the hiring manager is simply going to move on. In this market, you cannot afford to be put in the discard stack.