For OTA HD, all you need is a good UHF antenna, otherwise known as the BBQ grill. Make sure it is pointed to the HD transmitters because it is very directional. ;)
The CBS HD feed will be a national feed coming in through DIRECTV, not OTA. All you need is a DIRECTV HD receiver. If you have OTA HD, then you will have 2 CBS HD signals.
The CBS HD feed will come free to DIRECTV customers with a DIRECTV HD receiver before the Super Bowl.
To those who say the signal from cable, HD or otherwise, is better than satellite, just remember how cable receive their signal at the headend...