There's a great site with dozens of different mounts for various electronic goodies. And honest to gawd, it's called mountguys.com. I got a mount for my Garmin Nuvi that bolts to the passenger's seat, left front floor bolt. It has a bendable steel gooseneck (like electrical conduit) painted black, that stands 12-16" with a swappable mounting bracket on the end. Keeps my Garmin in a spot not far from where a cig lighter mount would, but leaves the cig lighter free to use as a 12v source, as intended. Doesn't block any vents, doesn't require any drilling, and it's good & stable.
Oh, and if you take the time to bend the conduit properly, you can keep it against the center dash, and out of the way of passengers' legs. No problemo.
$20, and they have one just like it for the iPhone/iPhone 3G, as well as most popular phones & GPS units.