Originally Posted by jimi_t
(And yes, it is spelt "Rakmaninov").
As to Mahler 8, two Symphony Orchestras is going a bit far. It's scored for one enlarged symphony orchestra (not a whole lot bigger than Mahler used generally), two choirs, a children's choir and soloists, which is a pretty large ensemble, but not the biggest there's ever been - Schoenberg's Gurrelieder, for instance, used a slightly bigger orchestra, along with two four-part male choirs, one full choir and soloists, if memory serves.
As to the question at hand:
Some of Rachmaninoff's Paganini Rhapsody is pretty wild.
There's also passages you could nab from Stravinsky's Rite of Spring.
Some of Liszt's Symphonic Poems would be good, and for relatively obscure stuff along the same lines, there's also Prince Rostilav by Rachmaninoff.
You could try the Dies Irae or Confutatis Maledictis from Mozart's Requiem.
Third movement of the Moonlight Sonata by Beethoven is a rollercoaster when it's played well (say by Daniel Barenboim in his first complete recording of the cycle).
Hope that's of some help.