Surface Pro Mini DisplayPort to Dual HDMI Adapter by Zotac works well
I just got the above adapter for less than $50 (S&H included) hooked up to a 27" Planar and a 24" Dell monitor. It displays well on both monitors and the mouse moves from screen to screen smoothly. The windows move easily from display to display. The SP appears to have the power to display 1920X1080 screens on the tablet screen and the two external screens as it is now.
I believe that Panos Panay said during the last Reddit conversation that MS is working hard on making Win 8 handle multiple monitors better than it does now.