I used Nulite rings (bought from Spruce) with a solid state dimmer (bought from Van's). I'm happy with that setup.

http://www.nulite.net

Spruce & Chief sell 'em, as do many other suppliers I'm sure.
 
Joe Blank said:
Give these guys a look too. I installed them on my -6. I was able to light all of my steam gauges and switch label using the 1 bulb system. Works slick! It was also less expensive v/s any other lighting method at the time. :)

http://www.sptpanel.com/fiberlites home.htm

I also used the fiberlites and really like them. The one problem is with the instruments mounted low in the panel, the rings block my view of the markings at the top of the instrument. If I'm really trying to hit an exact heading, I have to lean forward and crane my neck to see what the DG is really saying.

Other than that minor nit, I really like the system.

Karl