A neat accessory currently being showcased at Computex in Taipei, Taiwan is Weeview's Eye-Plug. This is essentially a camera on a stick. You plug it into the USB Type-C port of your Android smartphone, and it lets you shoot 3D videos.
It does the 3D capture thing by using both its own camera as well as your handset's, working together to record footage you can then view in a Google Cardboard headset. And because it goes into the USB Type-C port, you can plug it in either facing the front of the phone or its rear.
So yes, you can do 3D selfie videos too if you want to. Additionally, you can use the second camera for switching focus in post-processing or blurring backgrounds, for example, because it helps with defining depth in every shot.
The Eye-Plug will apparently be priced at around $35, which sounds very decent. It's still unclear what resolution its camera sensor has, though. Full production is coming later in the year, so there's plenty of time to find out. An iPhone-compatible model is in the works too.
Obviously the quality produced by this camera may not match that from your smartphone's built-in snapper, so color accuracy when going the 3D video route might not be perfect. That said, you shouldn't worry about your handset's camera not being center-placed, and thus not being aligned with the Eye-Plug - apparently the software that comes with the accessory will figure this out and compensate to keep the 3D output as smooth as possible.