What is an Alford Plea?

Much attention has been placed on the West Memphis 3 in recent years. Recently, an Arkansas judge allowed the three men to enter a plea agreement, known as an Alford Plea, whereby they essentially plead guilty but may still maintain their innocence. How does this work exactly? The Alford Plea arises out of a US Supreme Court Case that originated in North Carolina in 1970. What effect does an Alford plea have on you or your case?