I agree with alot of what's already been posted, but if you're dead set on getting a treadmill, I'd go with a Landice.
I currently own the Landice Pro Trainer with the extended L8 deck. The thing is like an aircraft carrier though....weighs 400lbs or so. But it's indestructible. I've had it for 5+ years now, and I've never even had to do maintenance on the thing. If you buy anything new from Landice, you'll pay a pretty penny for it (between 1k-5k, depending on model), so buy a used one. If you're looking for overall fitness, a gym membership is probably more worth your money, for reasons already stated by others. If a gym's not readily accessible, then you're best bet is to spend a little more money upfront and buy something that will last vs. buying a piece of cheap crap that won't make it through the year.