In case you didn't know, the absolute best picture you can possibly get for your HDTV (outside of Blu-ray) is from an off-air broadcast HD signal. In the airwaves, signals generally don't have to compete for bandwidth like they do in cable and satellite systems, where they're always compressed (sometimes excessively), which can lead to a degraded picture. So hooking up an antenna to your high-def set is a great idea, even if you have cable.
If there's any problem, it's that your sleek, modern flat panel is going to look mighty kitschy with a pair of rabbit ears on top of it. That's where RCA's Digital Flat Antennas come in. The first one in the line, the ANT1500, is basically a white square that's less than an inch thick. You can hide it underneath, beside, or behind your set, and it's wall mountable, too.
While the antenna's aimed at people who have old TVs that'll be near-useless after the analog switch-off next year, this is just the kind of antenna you want if you have an HD set without an antenna. For $60 (admittedly a chunk more than most antennas), it'll raise the game of a few of your HD stations (mainly the networks), plus you'll get all those digital subchannels you never see on cable. And you won't have to hide any rabbit ears next time you throw a dinner party.