The problem with HDTV tuners is the only hi-def signals you can currently get are broadcast over the air. There is no cable standard to get you a hi-def signal and I have yet to see an HDTV tuner with a DVI port.
For the time being standard def tuners are your only realistic option. And, sorry, If you want to do anything like an HTPC you want to stay away from the cheap tuners. They are usually not capable of working with the better PVR software out there. Namely SageTV and MCE. I personally don't like Beyond TV. It's the only one that supports the older TV tuners but is absolutely attrocious for CPU usuage when you do.
The cards I would recommend are the Hauppauge PVR cards. This
is the card that I would recommend. It is the cheapest PVR card by Hauppauge. What makes those cards different is that they encode the video to MPEG 2 on-board and keep the CPU from having to do that stuff. Basically the total CPU hit while recording a video using these cards is between 5% to 15% depending on the speed of your CPU.
Sorry about the HDTV thing but you are not going to find anything compelling in that area unless you want to be stuck watching your local channels in hi-def and having to deal with everything you would with an antenna sprouting from your TV.