It seems most of us thought this was some proprietary port that required their official adapter, but looking at the leaked pcmag review;
"Microsoft calls it a "Micro HD" port and sells a Micro HD-to-HDMI port adapter ($39.99 list), as well as a Micro HD-to-VGA adapter ($39.99 list). However, when we hooked up an off the shelf micro-HDMI-to-HDMI cable to the Surface, we were able to hook up to and use a HDMI monitor without any issues. The Surface supports extending Windows RT to the external screen, as well as mirroring the tablet's screen on the external display."
"Microsoft calls it a "Micro HD" port and sells a Micro HD-to-HDMI port adapter ($39.99 list), as well as a Micro HD-to-VGA adapter ($39.99 list). However, when we hooked up an off the shelf micro-HDMI-to-HDMI cable to the Surface, we were able to hook up to and use a HDMI monitor without any issues. The Surface supports extending Windows RT to the external screen, as well as mirroring the tablet's screen on the external display."