Right now ATI is the only one that has such a device. Unfortunately there pretty hard to come by because there only available to prebuilt systems, such as Dell, HP, and Sony. It looks like Sony is the first to break this "rule" by selling it seperately as a "VAIO Digital TV Tuner."
I heard a rumor that cable cards can only work with a special BIOS, and certified cable labs parts. But I would think that a USB device such as this would solve all issues such as this because wouldnt the device itself have its own BIOS?
Anyway.. its $299, and may still have some bugs in it. I want to buy one but its a bit to expensive for me to buy without knowning how well it works. I'm sure there is more information on it but I'm to lazy to check it out at the moment. But there might be some people on the AVS forum that may have used this device already.
http://www.sonystyle.com/webapp/wcs/stores/servlet/ProductDisplay?catalogId=10551&storeId=10151&langId=-1&productId=8198552921665246461&tab=Features
http://www.engadget.com/2007/10/25/sony-selling-the-ati-tv-wonder-cablecard-tuner-all-by-its-loneso/