There were about five minutes in the early days of LCD monitors when input lag for gaming was a major issue. It’s not something you should have to worry about these days with any TV that approaches half-decent. 60 vs 120 in general is a little more YMMV, but for most people and applications that’s not going to matter, either.
The big questions right now that will affect what general kind of TV you want are size, 3D, and connectivity/apps. In addition to that, you’ll need to decide your own preference between LCD and plasma, which each have pros and cons.
If you’ve got it hooked up to your PS3, you don’t need any of the big internet connectivity stuff, since you’re getting all of that through your PS3. Maybe it’ll be included in the best deal, but if there’s a great TV at a great price without it, that’s an option for you. 3D is a question that you’ll have to answer on your own. You’re not paying a huge premium to get it as a feature, but it takes you out of the running for a lot of the budget models from the better manufacturers.
I tend to think that there’s no excuse for a main TV smaller than 42 inches these days, if you’re sourcing it with HD material, which it sounds like you are. Brand wise, anything you’ve heard of is probably fine: Samsung, Sony, LG, Toshiba, and three or four others all make acceptable consumer level sets in a pretty similar price range. Stay away from the bottom of the barrel names and you’ll be fine. Anyways, recent sales for moderate feature 42 inch TVs lately have been in the $400-$500 range. We’re not talking super sales here, just the normal “hey, there’s a good deal on that this week”. Why does that matter?
… because we’re about to be talking Super Sales! T minus three weeks to Black Friday! Assuming you don’t need it right away, I’d definitely wait three weeks and take advantage of the single best time of the year to purchase a new TV. Even if you stick to internet deals and avoid the waiting in line, there’s a very good chance you could go to 46, 50, or even 55 inches with a good feature set for under $500 that weekend. You should see 42s in the $250-300 range. Bonus, you have a little time in the interim to figure out which features you really need. Happy shopping!