I'm not really recommending it--there may be better cams out there, but I have a Garmin Dashcam 55. I'll go over some of the pros and cons:
Pros:
+Good quality video
+Good viewing angle
+Has a special "parking mode", where it will record after you've shut the car off for a period of time (I have mine set to 2 hours).
+Aforementioned parking mode has a feature where it will shut down the dashcam if your 12V battery drops below a certain threshhold, which is adjustable to some extent
+Has some safety features (all of which can be disabled if you don't want them): collision warning, lane departure warning, and an alert that the car in front of you has moved.
+Has GPS so the recorded videos show your current speed and position
+Has two mounting options--either a metal disc you adhere to your windshield that the dashcam attaches magnetically to, or a suction cup mount (sold separately) if you need to regularly move it between cars.
+Stable and reliable
Cons:
-Its power connector is MicroUSB, which makes you think you could power it with any random microUSB cable. But Garmin uses a specific pinout in its cables, so a "standard" cable won't work. You either have to use their cables or find/make cables to Garmin's spec
-The aforementioned "parking mode" requires you to buy a special power cable intended for that purpose. It's a good cable and has lots of length to be able to hide it, but they charge like $30+ for it, which is a bit of a rip-off IMHO. You will likely need to buy a couple of "add-a-fuse" adapters to get it connected to both an always-on circuit and a switched circuit.
-Inexplicably, Garmin provides no way to choose how much of the SD card's space gets dedicated to parking mode videos. So they accumulate to take up most of the space on the card. As a result, the movies recorded during driving aren't kept as long as you might want, because older ones are deleted to be able to record newer ones. I expected Garmin to fix this with a firmware update but they never did.
-It has WiFi, so you can view videos on your phone, but the process of enabling it is annoying (pressing tiny buttons multiple times). The dashcam has voice control for things like "take a photo" or "start a time lapse". You'd think they would have thought to add one for "enable WiFi".
-It has no built-in polarizer to reduce glare, but at least Garmin makes one you can buy as an add-on that fits over the lens. Yet another accessory to buy.
All in all it's a mixed bag for me. I think the hardware is really good. Reliable operation and high quality workmanship. It has a lot of features too (how useful they are is another question). My gripe is that Garmin didn't really think through some of the features, and while there were regular firmware updates, none of them fixed any of the usability issues. They've stopped updating the firmware at this point (there's a newer model now).
But just as a dashcam that sits there and does its job reliably and unobtrusively? It's great.
I woud suggest poking around the dashcamtalk.com site and forum to see what other options are out there. I bought mine a couple years ago and there are probably better options out there at this point (including the newer Garmin models).