Is there an optimal size? Maybe it's just me, but the TV's over 50" just seem kind of obnoxious and the clarity is not as good. I seem to like the 42".
Any recommendations, or any good sites with reviews?
If you will be watching mostly HD, then 50" is definitely not too big (unless of course you are sitting less than 5 or 6 feet away). The thing with HD TVs is that most people get used to the larger sized screen pretty quickly, and then often kick themselves for not going larger. I picked up a new TV this summer. The original plan was for a 46 inch, but ended up with a 58 inch. No remorse for going too big. Plus, there are a number of decent 50" sets that you should be able to grab for around $800 these days.
For general TV viewing I tend to recommend plasmas (personal preference). I think they are generally better bangs for the buck, as long as your environment is somewhat light controllable. (though after spending some time with the Samsung pn58C6500 set, I can vouch that this is much less of an issue than with many of the older plasmas)
For around the $800 to $850 mark, the Samsung PN50C550 is a pretty good set. And for ~$200 more is the slightly higher end PN50C6500. The latter is nice if you want to wall mount, especially in the living room as it's just over an inch thick. It also purportedly has somewhat better picture quality than the pretty decent PN50C550 (though this has been a point of contention on A/V forums such as AVSforum). I would expect to see these prices discounted somewhat as we approach Black Friday.