bikesdirect.com seems to have good quality bikes for cheap. Not as cheap as X-Mart, but cheaper then your LBS. I've seen several from a distance and one up close. I'd recommend them. And you don't have to go any farther than your PC to buy. Drawback? You do have to do some minor assembly when it comes.
In any event, you'll want to get something with slick tires. Off-road, knobby tires will get irritating quickly when riding on the road: they're harder to ride, requiring more energy, and produce alot of numbness-inducing vibration. You'll also want a road-handlebar, not a flat, mountain-bike bar. Flat bars will cause tingling and numbness in your hands due to the reduced positions and the greater vibration from the tires.