The Crocs online store has a selected range of styles that you can buy 2 for $54.99. To qualify for the discount, just add 2 of the valid styles into your cart the discount will automatically apply. For example, they have the Duet Sport Clog on sale for 64.99 but when I add 2 pairs to my cart, they come down to $27.49 each.
Pretty decent savings to be had if you are in the market for some crocs. Some styles have run out of sizes but at the time of posting there are still a good range of sizes left in some styles.