I heard LCD pixelation was caused by signal clarity or speed...
(most commonly improper cabling)
For instance if you have a 1080p and the blue ray player...
Even at that high a quality, a fast action movie will not pixelate
Signal clarity on a digital signal should not matter. That is the point of digital, you either get the signal or you don't. You can have noise on the line and it won't make any difference to the picture... that means a $10 generic HDMI cable will give you the exact same picture as a $200 shielded cable. This is just a marketing gimic to sell you expensive cables. Cables are important in the analog world - not so much in digital.
Pixelation is because of low refresh times of the display. LCD's are a lot better at this than they were a few years ago.
Before getting a plasma, look at your room. If there are lots of windows or a lot of light in the room, you might be better off with an LCD. It doesn't matter how great your picture is, how good your contrast ratio is or how awesome your colors are if you can't see them because of the glare from reflections coming off the screen.
Personnally, I have a 47" Vizio 1080p LCD. It's not the best screen out there but for $1600 (Costco), it is the best bang for the buck I could find.