ok, I followed my own advice and ordered a trailtech striker to monitor voltage. It records high and low voltage, too, which will be nice to see. Also got it as a engine temp gauge (I got the one with the 19mm inline temp sender) and it the max temp of the day. Also shows ambient temp. Not sure what, if any, other info I'll use off of it, but when looking at the other separate gauge options, they totaled the same cost.
Will be nice to monitor that voltage under different conditions (load and rpm).
Lot's of different models (with different temp sensors, speed sensors, etc, but this is the one I ordered). Will be interesting to see if there is a way to mount the speed sensor to the brake disc and calibrate it to be even somewhat accurate. Not to worried about it if I can't, though, as the voltage, engine temp, ambient temp, hour meter, trip hour meter, etc are worth it).
http://www.trailtech.net/digital-gauges/striker/striker-kit-71-102-silver
Here are two other units I thought about that report voltage via a single multi-colored LED and also temporarily show conditions while the bike is turned off. Both of these are very slick and don't take up much, if any, dash space since it's only one LED light.
http://clearwaterlights.com/infopg_cvs.html
http://www.signaldynamics.com/heads-up-voltage-monitor/