I second the Shostakovich reccomendation. the 5th, 8th, 11th and 12th are all very exciting symphonies.
Verdi's Requiem is excellent as well, with a very powerful Dies Irae.
Some Mahler [would be] good [for your purposes] as well, particularly the last movement of the 1st, the 2nd, the 6th and the 8th symphonies. the eighth symphony uses an expanded orchestra along with about three choruses and an organ for a total musician count of ~1,000 performers. i know of no other peice that compares in terms of pure aural assault.
Bruckner's 8th and 9th symphonies would be an obvious reccomendation as well. both are quite powerful (and quite loud).
Then theres always Beethoven's 9th symphony...
EDIT: clarity injection