After seeing the sick battery monitor grant installed, i am looking to do something like that on my boat.
http://cgi.ebay.com/ebaymotors/CUSTOM-DASH-DIGITAL-DC-AMP-VOLT-METER-CURRENT-SHUNT_W0QQcmdZViewItemQQcategoryZ33681QQitemZ80702 67019QQrdZ1 I found this on ebay and although it doesnt do the calculations for you it would incredibly useful to see the amps your system is pulling at different volumes and another probably more accurate volt gauge. With a littel custom fabrication i think it could be a winner.
Let me know if you have any thoughts for ideas.