This is a very highly recommended HDTV antenna that costs less than $40. I've just ordered one and will write more once I've had a chance to use it.

Update: This antenna works very well, picking up at least 10 digital channels clearly even from the floor of my ground floor apartment in Santa Monica. Placement is important, so if you can't put it outside or next to a window with at least a partial view of the sky, I'd avoid an antenna. But if you want free TV and are willing to buy coax cable and do the work to mount the antenna, this is a great choice.