Try the custom AI to help you find products that Reddit loves.
I bought this and love it: https://www.amazon.ca/PAPAGO-GS260-US-Dimming-Dashcam-2-7-Inch/dp/B00KOUJO12/
Pricey but amazing camera quality and looks super slick with the screen built into the mirror, and even the rear view mirror part is superior to my stock mirror (Mazda 2).
Definitely gave me some peace of mind, although the only accident since was a hit in run while my wife was at the dentist, and the camera is off when parked. :(
Not OP, but I have this dashcam and absolutely love it. 1080p, awesome convex rearview mirror. Daytime video is so clear you can see bugs on the windshield, nighttime video is not quite as good. But overall I like it.
I got this one on Cyber Monday. They are listed $99 today, but it looks like used ones are cheaper. The mirror attaches to exiting one and the wiring is easy to hide.
I like the mirror because people don't know its there. I don't have to worry about people breaking in my car to steal it or changing the way they act knowing that they are on video.
If you want to get fancy there are other ones with multiple cameras so you can video tape the police officer speaking to you when you get pulled over. The police have no idea it is there. They also sell GPS attachments so you can track where you were.
I'm using this one and I can't recommend it enough: http://www.amazon.com/GoSafe260-GS260-US-Rear-view-Dashcam-Display/dp/B00KOUJO12
It doubles as a rear view mirror too that simply attaches over your car's mirror, making the camera very discrete. It also plugs into your car's power outlet so it turns on whenever your car is on.
There are some that are built into rear view mirror which are pretty well hidden http://www.amazon.com/GoSafe260-GS260-US-Rear-view-Dashcam-Display/dp/B00KOUJO12/
It's not cheap but I love it - PAPAGO GS260-US Gosafe 260: https://www.amazon.ca/gp/product/B00KOUJO12
If you're willing to spend a little more, I'd highly recommend the Papago 260 dashcam. The camera shoots high quality video and audio and doesn't look too noticeable from the outside (if your worried about theives). The video screen also doubles as a rear view mirror : http://www.amazon.com/GoSafe260-GS260-US-Rear-view-Dashcam-Display/dp/B00KOUJO12