Newegg offers the refurbished Asus Dual Band 802.11n Wireless N600 Adapter, model no. PCE-N53, for $24.99. Coupon code "AFEX327A0035" drops it to $9.99. With free shipping, that's $27 under the lowest total price we could find for a new unit elsewhere. It features data transfer rates of up to 300Mbps. Coupon expires April 1.
A 1-year warranty is included, although it's unclear who backs it.