All4Cellular knocks up to 84% off select Motorola Atrix HD accessories. (Discount is reflected on product page.) Plus, take an extra 20% off via coupon code "A4C20". That's the best discount we've seen on these accessories at All4Cellular. Shipping adds $2 or get free shipping on orders of five items or more. Deal ends January 20.
A best bet is the OtterBox Defender Series Case for Motorola Atrix HD in Black/Gray (pictured) for $19.95 before coupon, $15.96 after. With $2 for shipping, that's the lowest total price we could find by $12. It features a rubberized exterior, holster, and access to all ports and buttons.