With an 8' viewing distance, the ideal screen size for a 16:9 diagonal picture is 71.6" according to THX. This is given awesome source quality. SMTPE (Dolby labs) recommends a MINIMUM of a 59" screen at this distance, again, holding source quality as a constant.
This being said, I think that with 95% of your source being digital cable, I'd be comfortable with recommending an ~50" TV from that distance. The lower the quality of your feed, the smaller your TV should be to compensate.
I would, however, suggest that you visit a local Best Buy or Circuit City to verify that this is a comfortable size for your viewing distance. Bring a tape measure. In general, you should measure out the distance, and then pick a TV size that feels just a tad bit TOO BIG. When you get a TV home, in time, in tends to "shrink" (in terms of how it feels in your viewing).
Anyhow, here are a few TV's you may want to consider:
$2163.47 shipped: Samsung HLP-5085W 50" DLP (uses HD2+ chip, which is better than the HD3 on the HLP-5063W, plus it comes with a built in stand):
http://www.idealav.com/item.aspx?pid=80138
$1799.06 shipped: Toshiba 52HM84 52" DLP (uses HD2+ chip as well):
http://www.6ave.com/product.jsp?x=52HM84&zipz=11001
$1895 shipped: Toshiba 52HM94 52" DLP (again, uses HD2+ plus has built in ATSC/QAM tuner):
http://www2.buydig.com/shop/product.aspx?sku=TB52HM94
There really is no ideal solution. You have to pick a budget, then try to find the best TV for you, for your viewing source, for your viewing conditions, for your preferences.
