Someone already mentioned my thread in the DIY section but I'll post it here too. I built a mount out of balsa wood from the local hobby store to fit in the cubby left of the steering wheel. Took maybe an hour to build and works great and doesn't damage the car at all. I painted it with this plasticote stuff to help it blend in. Then I just screwed my navigon mount right into my custom base.
I use an old navigon 2100 hacked to run iGO 8. I love the iGO software. IMHO it's the best software out there and I've tried all of the major ones and most of the less heard of ones.
I now have one of the Verizon Droid ERIS phones and plan on modifying my mount to mount the phone horizontally so I can use the Google Navigation when it's available for the phone. In the mean time I'll just keep using the navigon.
The funny thing about the mount... I designed it to sit flat in the cubby and be completely flush with the top. Unfortunately, I didn't follow my own instructions and built it backwards lol. Now it sits a bit at an angle and isn't completely flush but still works well lol.