May 1 marks the 25th anniversary of American Airlines' frequent flier program, generally considered the first airline mileage reward plan. Since 1981, customer loyalty programs have exploded. Consumers under 30 probably don't remember a time when you went to a supermarket and bought groceries — or fixed your car or checked into a hotel — without showing a customer loyalty card.

But do customer loyalty programs actually work, especially for small businesses? Can you implement one — cheaply and easily — in your company?

For big corporations, the value of customer loyalty programs is hotly debated. Consumers are now overloaded with programs, frustrated keeping track of points, or just plain jaded. And it doesn't necessarily make you more loyal to your airline when you can never actually secure a reservation to use your frequent flier miles.

But for small companies, especially retail and service businesses, loyalty programs can be an effective and simple way to keep customers coming back.

The key is to keep your loyalty program simple, and be clear on what you hope to achieve.

The best reason for a small company to implement a loyalty program is to keep clients coming back. As a small business, it's hard to compete with the big box stores or corporations with large advertising budgets. Offering a simple reward punch card at your sandwich shop — for instance, one free sandwich for every 10 purchased — may keep a customer from going across the street to the fast-food joint.

Loyalty programs that work well for small businesses: