*AIW9800 has very good PQ for watching TV.
*Most recent ATI or Nvidia cards work perfectly fine for watching TV with an additional Tuner card. The newest cards feature Purevideo and AVIVO have advanced video decoder features.
*VIVO cards from either ATI or Nvidia will allow you to hook up your cable box, analog cable feed, sat dish ect to watch TV on your PC.
*TV Tuners come from a variety of vendors both hardware and software encoders.
*The Hauppage 150/250/350 are essentially the same, the 150 is newer and cheaper, the 350 features a nearly useless hardware decoder TV output otherwise is the same as the others. The 500 features dual analog tuners. All work best w/ a decent software like SageTV/BTV or with MCE 2005.
*Nvidia TV tuners; hardware: NVTV has single and dual tuner models; software: personal cinema was discontinued after the 5700 model.
*ATI software tuners: AIW = best all purpose single card solution, TV Wonder....mostly craptastic. Hardware; eHome Wonder uses same hardware encoder as hauppage 150/250/350 but less software support. great for SageTV and MCE 2005, discontinued. Theater 550 cards are excellent, arguably the best analog hardware encoder cards. Best for MCE 2005 and other PVR softwares.
Then there are a variety of excellent solutions worth researching. Leadtek makes popular software tuners that are perfectly good for watching TV, I see Peter recommend Lifeview often as well.
Hardware encoder cards are more suited for PVR duties than simply watching, although they are fine for watching as well, just probably overkill. They really offer not much over software encoder for just watching, and are generally poor for console input because of the output delay.