Easily In the Presence of Enemies Part 1/Forsaken/Constant Motion. In fact, I would put it in the running for best three-song run in the entire discography. I'm not sure it is the best, but I am really hard pressed to think of many three-song runs that are as strong. If only the rest of the album was anywhere near this consistently good as these three songs.
EDIT: Yeah, after taking a quick look at track listings, it's interesting to note that my "best 3-song runs" come from the most recent half of the discography. Here are the others I would put up near the top:
Misunderstood/The Great Debate/Disappear
The Great Debate/Disappear/Six Degrees
Vacant/Stream of Consciousness/In the Name of God
Never Enough/Sacrificed Sons/Octavarium
This is the Life/Bridges in the Sky/Outcry