I only started listening to Tool a few months back and have since fell in love with their music. I especially love listening to them while doing tedious soldering work. Like most others have said, it's hard to pick an absolute favorite, but my top few would have to be Vicarious, Lateralus, Ænima, 46 & 2.....well, I could keep going until I've listed every song of theirs in my library, so I'll cut it off there.
oldish topic, i know