You can easily get good TVs online on the cheap by browsing deal sites such as fatwallet.com.
I would recommend taking into account what people have said about contrast and response time. Response time is especially important if you'll be watching a lot of sports as some bad tvs may blur the image a little bit.
It's very easy to check for TV reviews, just type the model number into Google.
If you're looking for a budget TV, I have had very good experiences with Westinghouse. I bought myself one and also, one for my parents and I've had almost no trouble.
I haven't kept up with the TV broadcast signals, but it may not even be that important to get 1080p yet and you can save there too (unless you're going right to Blu-ray). The last football season, and college basketball season, the highest broadcast I saw was 720p (Fox) while CBS, for example, was mostly in 1080i. This may change soon, but I don't know. I also have had lots of people say that at 42", the difference between 720p and 1080p is almost not worth the cost.
It's good you're doing research. Just be patient and make sure you'll get a TV you enjoy.
Edit: Another thing: under NO circumstances should you spend money on expensive HDMI monster cables and such. Go to monoprice.com and save yourself a bunch while at the same time, losing no quality.