I just picked this up the other day (but from WalMart; was a couple of bucks cheaper, but I don't see it on their site, anymore):
Amazon.com: Arkon Mobile Grip Windshield and Dash Mount - Bulk Packaging - Black: Cell Phones & Accessories
It has a nice, spring loaded back piece that hugs the RAZR quite well even without a case, but I daresay it would also work well with a case. I use this on my car windshield to do GPS and Torque (*****in' app; I'll do a review on it as soon as I get some photos and video). Doesn't shake at all; even uder high boost on a rough road Also, it's a very understated, handsome looking mount. Even though it's a universal, it's sleek and svelte; doesn't look at all unwieldy or bulky. In fact, It looks sleeker than the purpose made dock for the RAZR (though it obviously doesn't come with cords). The movement of the mount, for viewing angles, is very firm without any signs of give, yet compliant enough for fine tuning. It feels as though it will hold firm for the long haul, but only time will tell. At $12, though, it could only last a year and I'd still be pleased with it.
I haven't tried the mounting disk, yet, but I will so I can use my RAZR as a HUD with Torque. I see no reason why it wouldn't work equally as well as it has done mounted to the windscreen. All in all, I can't recommend this any higher for an inexpensive mount that does the job of mounting your RAZR to your car.