Which is the better gaming display? A top of the line plasma or a top of the line LCD?

It's very debatable. The best option is to take your 360/PS3 into a Best Buy, or use one of theirs if they have it out for demo, and play on both. For real. Personally, I use a low-mid end LCD, and I'm very happy with it.

Rear-projection. I've been gaming on my sony LCOS set for a few months now & loving it. Cheap too, much cheaper than equivalent 50" lcd/plasma 1080p.

The room in which you plan to use it is a big factor.

My living room is bright and has many windows. A plasma screen is generally too reflective, I needed a matte LCD screen otherwise I would have seen too many reflections.

I've read that any static image elements (common with games) will burn into the screen for plasmas.

I've read that any static image elements (common with games) will burn into the screen for plasmas.
this can happen with lcd's too, but it takes a lot longer for it to happen.
and my chouice would be front projection lcd (hey, you never mentioned if it has to be a flat panel display or not ;)). nothing beats playing games at 100+ inches. although if 3 chip dlp's drop down in price i'd go with a front projection dlp unit.