ElGato makes several varieties of EyeTV. I got an EyeTV 200, which has firewire 400 interface. You can plug it into either Cable or RCA (as in from a VCR or satellite box). I believe they also make an HDTV version with a built-in antenna.
It's a great product. Pause live TV, convert to quicktime, edit out commercials, import it to Toast and slap it on a DVD. I remember going out of my mind trying to describe Most Extreme Elimination Challenge to a friend with no TV... I just recorded four hours of an MXC marathon, edited out the commercials, and, well, you know the rest. I also use it quite a bit in recording documentaries and the like for my classes.