I want to look into purchasing a starter Mountain Bike, mainly for exercising and some trails around here (but not for a little while). The main reason really is to try to get back into shape, as some of my close friends around here have noticed that I gained a few extra pounds... LOL I honestly have no idea where to even start looking, as I haven't done that since I was 15 or so. Can anybody suggest what to look for, prices, models, etc.? I don't plan on making this a serious hobby, so don't want to go crazy with the price. I noticed even Wal Mart has some nice-looking ones these days, but don't want to buy something completely in the dark, which could end up caught under a tractor trailer... with me on it. 
So...any ideas?

So...any ideas?