xtreme, the song that got me started was the song "panic attack", but then i started listening to more of their stuff. Metropolis part 1 is full of crazy time signatures, and Dance of Eternity is insane as well. almost all the stuff they play is polyrhythmic or in odd signature.
watch some of his youtube videos, ill post one here:
he uses an ostinato in this song... that takes some crazy limb separation
in addition to all the odd rhythms, theres so much technicallity.
interesting update here, portnoy is going to record the drums for A7X in the studio, since James Sullivan is dead
im not sure if im happy about it.
anyway, tool is really good, too. danny carey does some pretty wierd stuff, but way different than portnoy.