You can add external LCDs using a DVI-D to TTL/LVDS adapter. These can be found at
http://www.aaeon.com/PD_Products_Detail_AEEE87FC762C45F1AC_F67467B5A6BD44F0B9_30D6012CD30E4BAAAC_US_utf-8.html
http://www.digitalview.com/brochures/ALR-1400%20brochure.pdf
I know the ALR-1400 works for sure, but it really depends on the display you are using. There are three different versions depending on the resolution.
Gerald