After my stator failure earlier this year, I started thinking it would be nice to have a voltmeter on the bike to catch a charging system problem before it causes worse problems. I found this voltmeter on eBay:
http://www.ebay.com/itm/Car-Motorcycle-LED-Digital-Display-Voltmeter-Waterproof-Meter-12V-24V-Hottest-/311325532444?pt=LH_DefaultDomain_0&hash=item487c72a11c
It comes with a handlebar mount, but I didn't find a good place for it. I took it apart and found that the mount and holder were about 5 times bigger than the voltmeter itself.
So I insulated the meter's terminals with electrical tape, and looked for a better place to mount it. Lo and behold, it fit between the instrument panel and headlight plastic like it was made to go there. It fits there snugly without any other means of support.
To wire it, I attached the ground terminal to one of the bolts that holds the insturment panel in place, and spliced the positive lead into the fuse block main feed wire.
Edit: When I went to eBay to get the link, I saw that you can now buy just the voltmeter without the handlebar mount!
http://www.ebay.com/itm/12V-24V-Car-Motorcycle-LED-Digital-Display-Voltmeter-Waterproof-Meter-GN-Hottest-/141585436481?pt=LH_DefaultDomain_0&hash=item20f7264f41