I think it's going to be impossible to get 10 reference albums let alone 5 that we can all agree on. And compiling a list of Only ten is like pulling teeth.

My ten Must haves:

Deep Purple- Made in Japan
Jean-Michel Jarre- Magnetic Fields
Klaus Schulze 'X'
Porcupine Tree- Arriving Somewhere
Ten Years After- Live at the Flimore East
Iron Butterfly- In-A-Godda-da-Vida
Mike Oldfield- Tubular Bells III
Golden Earring- Moontan
Grand Funk- Caught in the Act
Emerson Lake & Palmer- Show that Never Ends