Don't need to get too technical over dash cams. Both the GF and I run Genius brand, only forward facing but meh. She has this one.
http://www.memoryexpress.com/Products/MX49049
Hide the cables as well as you can, plug it in, and it powers up with the car. No need to touch it - most are like this anyhow. Mounted to the window, the view is pretty much pillar to pillar. You can get a little fancier and go for a cam with front and rear view as well.
Spend a little extra on a larger SD card. Once the card fills up, it will start overwriting automatically. Have a second one handy in case of accident or what not. If I record something I want to keep, i'll switch cards.