Most companies do not have a way of encouraging referrals actively, although they welcome them when they come around.
There are, simply, two parts to getting great customer referrals.
The first concerns the quality of service or product. Nobody is going to talk nice about anything you did for them without it having been one-of-a-kind, or at least easy, cost-effective and friendly. Customer feedback sourced at two different points after the sale is made should be used to improve the process and product. Even if the product is good, the process that a customer goes through is just as important. People should not be on hold when ringing through, and should be treated with the utmost respect. You must assume the role of trusted advisor to ensure that what you say strikes a chord - every time.
Secondly, you must encourage referrals in a fashion that is comfortable for you and the customer. Even better, the customer should not be aware that you're even doing any prospecting through them. He or she should land on the thought and determination autonomously. This will ensure maximum enthusiasm on their part. Again, how do we get them to feel the urge to proclaim your greatness to the world? A great product, great process, great people!
Sometimes, though, people like to know that you are on the look-out for referrals.
Most people like helping other people, so via them referring friends, you are improving their own happiness, as well as increasing your revenue on the cheap. You should be clear in your questioning regarding referrals (if that is your angle); your customer must be made aware of the best process or material to use (forwarding a certain e-mail, providing a telephone number, etc.), and should be encouraged to actually make the yes/no decision. Do not force anything, just let them know that a lot of business is gotten via referrals and since he/she is happy with the service, "here are some ways to tell others..."
Let's recap: all other things aside, you must be confident in your product and you must be comfortable with facilitating the word-of-mouth and lead-referral system. If everything seems natural and if the customer makes the decision by themselves, you can expect a large number of referrals.