I used Rock Band 2 and it's photsensitive guitar for these tests. It is VERY accurate and repeatable. I was able to confirm this by testing it with a CRT first. The best thing is that it is SIMPLE and has virtually ZERO points of failure for stupid people like me.

I've posted these results in a few other threads. Bottom Line: Samsungs SUCK for lag.
I finished up my testing on on these three devices: An old Panasonic 32" CRT, A Samsung A580 52" LCD flat panel and a Sanyo Z3000 projector. Used the Rock Band 2 calibration system.
As expected the CRT has ZERO lag. Rock Band actually measured it as -3ms.. yes NEGATIVE 3ms. Now that's fast! LOL. If you are a competitive twitch gamer... CRT is your only option, I guess. I used SVIDEO and 480i for this test.
The Samsung A580 is a 1080P 60hz non-FI (Frame Interpolation) Best Buy exclusive model I got last year on their Black Friday sale. It's the same as an A530. This got 65ms lag time. ( I'm wondering if Samsung needs to work on their circuitry, because my friends 720P non-FI Samsung Plasma did even worse than this, 77ms lag time! )
Next up was the Sanyo Z3000 1080P 120hz FI-capable projector. I just put this in my home theater which I use for all my gaming, so I was a bit worried about what I'd get for results on this after seeing the bad numbers on the theoretically simpler Samsungs as pointed out above.
Turns out there was no need to worry. Even with the FI (Smooth Motion) turned on high, the lag was only 48ms. With the FI turned off, it improved to 30ms. Very nice.
So, there are some more data points for people to mull over. I will say the 77ms delay on my friends plasma was slightly noticable in Rock Band, I don't know if the 30ms will be that bad.
I found it interesting that a "High-End" 120hz FI projector was faster than a "low-end" non-FI plasma or LCD.
People with Rock Band 2 should start posting more results from their displays.