Well, I have been doing a lot of research lately also on similar sets and I'm probably driving myself a little crazy in the process.
Here are my thoughts on the sets I have been looking at and am currently having difficulty deciding between;
Samsung FP-T5084 50" 1080p Plasma;
This TV seems to have everything; great HD picture, great blacks, high resolution, good connectivity and so on. My biggest concerns are the silly looking large plastic bezel and the reflectivity of the screen. But for HD movie performance, it's as good as I've ever seen. The only better picture I have seen is on the $5000 Pioneer.
Panasonic TH-50PZ700U 50" 1080p Plasma;
This is Panasonic's entry into the high-res 1080p plasma field. Great HD picture, great blacks, only 2 HDMI. I really can't tell much difference between this and the Samsung in PQ, and the price of the Panny and the Samsung are basically the same at $2300.
Sony KDL-46XBR4 46" 1080p 120Hz LCD;
The newest offering from Sony is probably the best LCD on the market today. But whether it has a better picture than the above plasmas is not easily apparent to me. I haven't been able to find a shop that has this TV next to any of the other TVs I'm interested in, so I haven't been able to do direct side-by-side comparison, but from what I see the Sony is very impressive. The price is still high though, about $2700. Is it worth $400-500 more than the Plasmas? Probably not, especially since the screen is 4" smaller, but it does have a key advantage - a non reflective screen. Depending on lighting, this may be a key consideration.
Samsung LNT4671F 46" 1080p 120Hz LCD;
Another impressive LCD as far as LCDs go. But the typical oversaturated color issues are still noticable. I like this TV, but can't help noting the Plasmas have better HD movie color and PQ. I don't really notice the difference that 120Hz makes over plasma or other 60Hz panels, but I haven't really spent a lot of time evaluating it either. Priced around $2400, I still don't see why I would settle for 4" less screen realty vs. the 50" plasmas.
I have also seen the Samsung 81F LED Backlighting series, but again not side-by-side with any other TV so I couldn't really discern the differences. The 81F however does come with a very steep "coolness" upcharge for the LED feature, putting it near $4000 for 46" of screen real estate.
At this point I'm leaning towards the 2 plasmas at the top of my list. I have to go look at them again. My viewing area has a double french door directly opposite the wall the TV is going to be on, and a large window to the right as well. However, the vast majority of my use for this TV will be nighttime viewing of movie material, so I'm not too concerned about the ambient light and reflectivity issues of Plasmas.