The technology of dash cams is progressing so quickly, the four-year-old one I have is pretty dated at this point. I did upgrade to a newer model about a year later and moved the original to the rear of my car, so I now have front and back views. You can get a really good one for about $100 now, and an adequate one (probably even better than mine!) for even less. For a really great price on one, daily deal site meh.com has them for sale every couple of months if you want to wait. Essentially, it's to the point where I think everyone should have at least one in the car.
Mine have already paid for themselves. I was sideswiped by a guy who was illegally passing me on the right on a 2 lane, 25 MPH residential street. I was initially getting push back from his insurance company about wanting to get both sides of the story. But after I sent them video of what happened, they promptly paid for the damage.
I also recorded a collision where a speeding car goes out of control, crosses the center line and smashes into an SUV (by far my most popular published video to date!). The police actually contacted me and thanked me for posting it as it helped them with their investigation.