Communion is a great example for polyrhythms within the music as a whole. For polyrhythms within the drums themselves, I'll give you a few examples to check out:
As mentioned earlier, Eyes of Medusa has a ton of polyrhythmic beats - 0:36-0:53 has a snare and high-hat playing in a 4/4 type of sound (for the groove), and a repeating bass drum pattern that is in a 3/4 type of time sig-Very interesting. Later on, 1:06, for the verse, same theory behind it, but this time, the bass drum is doing a pattern that sounds like a 5/4 time sig, starting on the up-beat... I think. This is pretty vicious
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(1:14-1:18 notice the awesome bass drum trickery - love it)
Accolade II - 1:19-1:30. This illustrates the bass and snare doing a pattern in 5/8, and a high-hat playing straight 1/4 notes.
Edge of Forever - 0:45-1:01. This is close to the same type of technique. Bass and snare creating mainly a 7/8 pattern, with a few alterations, and again, ride cymbal playing 1/4 notes.
Rediscovery, part.II - 5:31-5:44, a pretty complex beat in 6/4 - 5/4 alterations, loaded with awesome high-hat goodness, and then at 5:45, he introduces a steady 1/2 note ride over the existing beat. Simply amazing...