You can try to do what I started - go through web admin and pretend you are manually adding a device. By selecting a manufacturer, selecting TVs/Plasma/LCD/Projector from device category, then the auto filter checkbox you can look for specific models. It's cumbersome and doesn't give you good info like the Sharp Aquos line should be all plug and play as mentioned in this thread, but if you are looking to see if a specific TV is supported it kinda works. Having a list of TVs and what is supported out of the box would be handy. I'm really not sure if being on the list means it can be controlled via serial/usb, or if some are there that just have USBUIRT codes.
As for LCD vs. Plasma, there are plenty of discussions all over the internet on this one. Since I've been looking into it, here is my take. General consensus is plasma is the better option in the 47"+ range. Better picture, darker blacks, no issues with motion blur, with new tech very little chance of burn-in, better viewing angle, and in the larger sizes they are cheaper. This comparison doesn't include back-lit LED LCDs with local dimming and 4 color LCDs, which are or will soon be as good or better than both conventional LCDs and plasma in every way. Too bad they are sooooo expensive right now. The only real downsides to plasma are they do not do as well in a brightly lit room and they use a fair amount more electricity to run. So why do I want LCD? I suppose it's because I'm completely happy with my smaller LCD TVs and I'd rather give up a small bit of quality for no chance of burn in instead of slightly better picture with almost no burn-in issues. It's also worth noting that if you don't want/need it mounted on a wall a DLP might be a great option. My father has a 73" DLP (HUGE room, a 73" TV makes sense and is perfect for as far back as they sit). My initial thoughts when he said DLP were "meh" it's gonna suck. I was surprised, the picture is great.
BTW, I wouldn't limit it to rs232, I believe there are USB connections that are plug and play that can do everything serial can. Just note that just because it has USB doesn't mean you can control the TV that way.
edit: it would be great if there were lists of TVs, receivers, remotes, etc. and what works for each. I'd even be willing to put a list together if someone could tell me how to collect the info. ie - I can get the TVs by going through the add device wizard, but I have no clue what is supported in terms of USBUIRT/serial/USB from there.