I picked my top 10 customers and made them a part of the Think Tank of my organization wherein they contributed on new product/service ideas and suggested improvements on existing ones. One thing we ensured was that if a customer suggestion was accepted then the same was definitely implemented and shared with all the 10 of them. Special pricing and unique referral programs were extended to the top 10 for all the new products/services to which they contributed in the form of ideas. They bought the product/service as it was something they really wanted and they referred it since they were one of the creators.
Focus on the customer and customer experience, and the customer will remain loyal.
I mean, the focus should not be on "how do I make customers loyal to ME" ... instead the focus should be: "How can I truly and genuinely help my customers and make their lives better." That will generate a natural and "organic" customer loyalty.
I created a product that they just couldn't buy anywhere else. Until the competition caught up - by then I'd had a good 10-15 years of loyal customers.
I'd say there are three ways to strengthen customer loyalty.
1) Have a great service / product to start with. People don't want to buy something that doesn't work.
2) Provide top-class customer support for when things do go wrong (as they will). If you respond fast to customer calls or e-mails, and put mistakes right quickly and smoothly, customers will feel like you love them and want to help them. If you ignore calls or respond slowly, and if you come across as not caring if things aren't working for the customer, you'll lose customers quicker than you can say "Jack Robinson".
3) Listen when customers provide feedback - but remember you can't be all things to all men. As Jon Sherrington says, treat your customer like a queen, not like a king http://www.hydrogencreative.com/the-customer-is-queen-not-king/#comment-4019