Editors' note: As of July 2011, the Roku HD and Roku XD have been discontinued and replaced by the Roku 2 HD and Roku 2 XD, respectively.
The Roku XD ($69.99) and Roku HD ($79.99) are the step-down versions of the Roku XDS ($99.99).
The Roku XD is mostly identical to the XDS, except that it does not offer component video and optical audio output; it does not include the USB port (for future local media playback); and it offers single-band 802.11n Wi-Fi (not the better dual-band 11n found on the XDS). If you don't need any of those features, you can save $20 by going with the XD.
(Shoppers should note that the Netgear Roku Player NTV250 is just the Roku XD sold under a different brand.)
