Agreed. Start with Panasonic and go from there. It is the best value/picture for your dollar.
Consider the online stores of
Complete-It and
AVDeals. Both are Canadian, and both offer Canadian warranties. They do only sell the commercial versions (no speakers), but that only matters if you dont have any sound system to hook up.
I feel that the 50 inch is the best value. They are better resolution, at 1366x768 than the 42's at 848x480. You do see the difference. But, that being said, I'd take a Panasonic at 848x480 than a cheap knock off at 1366x768. If you can afford it, you can get True HD (1980x1080) with the Panasonic 50" for just under $5K (commercial).
Regarding cables, MonoPrice is the place to buy all cables. That is all you need to know there.