Scosche magicMOUNT Magnetic Mount
Check this out... works great with Nexus 5. I modified mine a bit so I could adapt it to work with my existing RAM mount setup on my dash, but I am pleased with the results.
One thing to note, however - the mount comes with a couple of steel plates, one of which normally needs to be mounted inside a case. If you don't use a case, you don't need a plate because the Nexus 5 has four steel discs built into the back cover already that the magnet in the magicMOUNT is more than powerful enough to hold on to. If you do use a case, you're going to have to use one of the plates because the added thickness moves the built-in steel discs too far away from the magnet for a good grip. If you use wireless charging, do not install the plate in the center of the case as it will block the induction coils and wireless charging will not work.
Instead, offset the plate to one end like I did.
You can get this directly from Scosche for $19.99 plus shipping at http://www.scosche.com/magicmount
and there are currently three different variations to choose from. Okay, on to the pics:
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