So that's what I ended up getting, the SM-310. It's a little frustrating, that I can't find many reviews/comparisons on different units. But this little guy works good! Window mount, dash mount and vent mount. Adjustable, and the mount itself does not block the 3.5mm jack, or the USB on the Droid (haven't tried the Eris yet). I turned it horizontal and drove for about 20 minutes that way, without any problems (better for me to have the usb port down, and the 3.5mm jack pointing left). Feels solid enough to drive like for long distances without it coming out.
Akron SM-310 for $19 shipped at Amazon for the win!