Hey Demoralizer!
i think that most of the clasical pieces uses
The basic major scale , which is also called the ionian mode
and the minor scale which is know as aeolian mode
the aeolian mode is basicly the ionian one , starting on the 6 note ...
the ionian mode is built in the next way:
I ii iii IV V vi vii°
The big letters is for major chord and the small is for minor...
example scale:
C D E F G A B C
from this one you can build any other , by replacing the C in the beginning by any other note...

hope that i helped you someway :)