I've found the auto mounts from "Proclipusa.com" to be very high quality and well designed. If you haven't seen them before you should check them out. They're a little more expensive, but are easy to install and look very professional. I recently emailed them to inquire about the availability of holders for the Storm and received the following response:
Thank you for your interest in our ProClip holders. At this time
we do not have a holder for the BlackBerry Storm. We do
anticipate making one, however due to the large number of new
products we are developing, we cannot give a specific date as to
when this will be available. You will be notified by e-mail as soon
as the holder has been received at our warehouse and is ready
for online ordering.
ProClip USA Customer Service
Toll free: +1 800-296-3212
Web: ProClip Mounting System x-xChoose Your Country
So there is hope for a high quality car mount! When I hear about the Storm holder being available I'll make an announcement here. I would also suggest that anyone else who's interested in one contact them... the more people who do the higher priority they're likely to put on a holder for the Storm.