A 1080p HDTV with HD cable/satellite blows away a standard 36" tube. However, when you watch non-HD programming on an HDTV it actually looks worse than a 36" tube, because you can see the pixelation and compression artifacts. So you'd be advised to pay the extra $10 per month for HD programming.
BTW, watching the NFL in HD is about as close to heaven as we can get on this planet.
When it comes to Blu-ray movies and PS3 games, the difference in quality with knock you over.