Plasma gives better picture quality than LCD but is more expensive, heavier, and costs more to run. Neither are light enough to mount purely on plasterboard: you must mount the frame onto the wooden frame behind or onto brick. Be careful of the colour depths. Some displays don’t give a full 8 bits (or more) per colour channel, leading to banding. Remember 16-bit colour on PCs?
Don’t be gulled by salesmen who tell you that plasmas will wear out. Their life expectancy - 50,000 hours or more - is only an issue if you’re going to have the display on 24/7. Plasmas can still suffer from burn-in, though, but not so badly as they used to.
Be aware of the difference in being able to take a 1080p signal and being a 1080p display.
Your display should accept 1080p at 24 fps for proper display of videos.
You want 2 or 3 HDMI sockets, which should be v1.3. HDMI is the HD display connector and carries both sound and video. v1.3 is the standard. If you don’t use HDMI your HD picture may be degraded.
You also want 2-3 SCART connectors for non-HD devices.
There are two main HD standards: 720 and 1080. These refer to the number of horizontal lines on the display. They come in interlaced and progressive versions. You want a 1080p display. This has a resolution of 1920x1080.
Next you should consider the size. Just like computer monitors, the measurement is along the diagonal. It’s not a case of the bigger the better, because if you sit to close the picture quality deteriorates. For me, sitting at 9-10 foot, 42"-50" is about right, but with a full 1080p display, they’d be fine at 6 foot for gaming. If you’re not buying a High Definition source, then you need to consider how Standard Definition pictures will display at your viewing distance. At 9’ distance, 42" is on the upper limit for me.
Your new DVD player should be capable of upscaling. Try and get one from the same manufacturer as the display so you can use the same remote for both. I’ll let someone else explain the difference between Bluray and HDDVD.