iTechDeals offers the refurbished Plantronics M55 Bluetooth Wireless Headset for $15.99. Coupon code "BLUETOOTH1" cuts it to $14.99. With free shipping, that's $16 below the lowest total price we could find for a new headset. It features Vocalyst service, Deep Sleep mode to extend battery life up to 5 months, and 11 hours of talk time.
Note, no warranty information is included.