I got Adventuretech mirror extenders with RAM ball mounting spot. They're pretty great. I recommend some LocTite Blue(non-permanent) once you get everything where you want it.
I'm running these eBay items on my XJR. However, having compared them with Richland Rick's extrenders on AstroBob's Strom, Rick's appear to be much stronger. I don't think mine would survive a good bash.