edit - 7/28 amazon changed price to $13.65!
Bracketron PHV-202-BL Grip-iT GPS and Mobile Device Holder (Black) - $4.19 free shipping available
I am currently using this exact same style but made by Scosche.
I have the DroidX mounted in the horizontal position with the vent mount and it is secure. Simply place your droid in bracket and close foam lined arms around droid. You can vary the tension and also the angle on the mount. There is a button you depress to relieve the tension and the droid comes out quickly. Picked up a few of these to give to others. Also includes another mount with adhesive to place a more permanent mount location instead of using your vent.