Can't do just one since visiting guests will come with different musical tastes, but....
1. I'll tend to pop in
ELP - Still You Turn Me On (2000 DVD-A) to BLOW people away with sheer loudness but with crystal quality. I have Definitive Technology towers with 500 watts of bass so the house literally shakes on that one...
2.
Gentle Giant - The Power & The Glory(just replaced all others on this list...) Screw 'em if they don't like the music. The production, clarity & mix are the closest thing to Heaven I've encountered.
3.
EJ - Capt. Fantastic DVD-A. Awe inspiring.
4.
ELP - The Only Way(from Tarkus) Steven Wilson DVD-A. If you think you have a powerful system, try this one as loud as it goes.
5.
YES - America (Fragile 2000 DVD-A) I love this mix plus the extra keyboard tracks. This is a guitarist's dream song.