JoshMc I have a few ideas for you!
C major superimposed with a F# major 1st inversion. Can transpose this of course. (turned out this was the petrushka chord)
Parellel major or minor triads with descending bassline. Bassline can descend chromatically, through whole tones, or through a scale. Just experiment to see what sounds good to your ear.
I have many more polytonal ideas that I have come up with (I'm not saying I'm necassarily the first to have discovered them), but I would be giving away too much if I went into more detail
You should obviously listen to Stravinsky as was mentioned, also try to listen to some 'golden age' filmscores/TV music if you can. Scriabin's 'The poem of fire' would be a good work to listen to, as well as his later works even if you don't enjoy them.
ablyth I havn't heard the Milhaud piece, but I think Stravinsky went too far at points throughout the Rite of Spring.
As for books can't really help you, but listening to polytonal music is as important as reading about it.