If you are treadmill shopping, be sure to look for one with a relatively strong motor, a nice wide deck that reduces impact, and has fans. We really like our NordicTrack treadmill for all of those reasons.

I have the tendency to overtrain at times (or just overdo it). Having a high quality treadmill will definitely reduce the risk of injury. Plus, it will make your indoor running experience much more enjoyable (or less miserable).

I went for one of NordicTrack's more expensive models as I wanted most of the club-quality features (durability, 12mph speeds, 12% inclines, and a wide variety of pre-programmed workouts). It also has a relatively shock-absorbing deck that is fairly wide. Believe it or not, a wide deck is very helpful as it is very easy to accidentally step off the treadmill and get hurt when you are watching a movie and running. Needless to say, falling off your treadmill would be a pretty embarrassing story to have to tell to your coworkers. I've had friends who've done this. I've even come close a time or two myself.

I'm also a huge fan of having fans on your treadmill. A little air movement goes a long way towards making the indoor running experience more enjoyable.