RadioShack offers the Roku Streaming Stick, model no. 3500R, for $39.99. Sign up for their e-mail list (the field is at the bottom of the page) to receive a coupon for $10 off, dropping it to $29.99. With free shipping, that's $10 under our mention from four days ago and the lowest total price we've seen. (It's a current low by $10. For further comparison, we saw two for $54.98 two days ago.) It plugs into your TV's HDMI port and streams 1080p video via WiFi.
Orders placed by December 22 at 11 am ET should arrive for Christmas.