Hey, remember the KWorld PlusTV ATSC 340U? (With a name like that, how could you forget?) It's a TV tuner that plugs into a USB port and pulls down over-the-air HD signals or unencrypted QAM signals (which are delivered via cable). The last time I posted it, Newegg was selling it for $14.99 after rebate, plus six bucks for shipping. Well, now you can get it for $14.99 after rebate, plus zero bucks for shipping!
This would make a killer second tuner for anyone already running, say, Windows Media Center with an analog tuner. The PlusTV is strictly digital, meaning if you plug in a cable-TV cable, you'll receive only QAM stations. (If you're not up to speed on QAM, check the Wikipedia entry.) What's more, Windows Media Center should be able to detect the tuner if you use an antenna (a small one is included), but it definitely won't if you go the QAM route (that's a WMC limitation). Fortunately, KWorld bundles Arcsoft's surprisingly decent TotalMedia software, which provides full DVR capabilities--and QAM support.
I've been watching the Olympics in full HD glory using a tuner very much like this one. If you don't mind waiting on a $20 rebate (PDF) (good through Aug. 29), you won't find a better price on an HD tuner for your PC.