www.partsexpress.com is the place I use just as often if not more often than crutchfield, though I get most of my stuff at dealer cost from my buddy Manny.
I think the size you want to use depends a lot on the car. If its a larger SUV type vehicle, the 7 inch units get easily dwarved by the rest of the car, whereas this might not be as bad in a sedan type installation. IMO, anything smaller than 7 inches isn't worth the money.
Over at T-Rex audio in CT we use mostly Farenheit stuff. They look pretty sweet, even the larger units look clear (17 inch wide screen that was put in the tailgate of a show truck). They're reasonably priced, too. I honestly wouldnt consider a TV tuner a big priority, as from what I've seen, very few channels come in. If you're interested, they even make a din unit that folds out of the dash if you have room the equivalent size of a stereo head unit.