Dolby or THX demo disk?

I hear that there are DVDs out there (you can't buy em directly, unless you're a dealer) which are great to demonstrate the capabilities of your Dolby or THX-capable home theatre systems. Does anybody have recommendations of specific DVDs or places where you can get em? Note: sorry if this has appeared on this board already, but I tried doing searches for it and the search engine kept crashing.

Just search google for or the many variations on it(like replacing dolby with THX).

I know you can get demo disk at best buy and other DVD retailers. they have demos of sound, picture clarity test and video clarity demos on them. If you really want to show off a 5.1 system put in the Saving Private Ryan DVD and play the 1st beach storming scene with all the bullets wizzing by and stuff. :)