So much stuff to cover, so I'll start with the two most recent albums.
Inferno, 0:13 - I love the main bass/drum groove; it's time is constantly shifting and it feels very chaotic yet still manages to have a recognizable "groove" (something DT has trouble doing).
Wicked, 0:05 - Obviously, this groove is sick.
Accolade II, 4:40 - This nice easy section is a great off-time bass/drum groove.
King of Terrors, 0:54 - Simple yet effective, and badass.
King of Terrors, 3:29 - Probably the most metal I've heard Symphony X get, pre-PL.
Awakenings, 3:10 (and all the verses that use this riff in different keys) - It's like a funky metal riff; it reminds me of a more intense "Gates of Babylon" (old Rainbow) groove.
The Odyssey, 8:24 - Simple groove, but metal and tight. I love how it sometimes ends in 5/8 to make it sound tense and uneasy.
The Odyssey, 9:21 - The bass playing the riff from before and the guitar being funky. Love it.
Frontiers, 1:12 (1st verse) - Shame this song didn't make the full album, because the bass groove here is awesome.
Set the World on Fire, 0:20 - Main riff of sorts; too bad they didn't use this more in the song as it kicks all sorts of ass.
Domination, 0:44 - When this groove kicks in, badassness erupts from all speakers. It's just so powerful.
Domination, 4:12 - Love this section, although I can see how some may find the guitar annoying. But the bass/piano groove is so great and sinister-sounding.
Serpent's Kiss, 0:02 - Well, obviously. The verses that follow it are great, too, but the bass should've been turned up. You can barely hear it.
Paradise Lost, 0:50 - Similar to the "Frontiers" verse in the bass/drum department, made even better by the great piano line.
Eve of Seduction, 0:46 - This is a great riff, and a great groove.
The Walls of Babylon, 1:04 - I love when the main riff goes into 6/8 here. It's a great changeup for a riff that was already badass in 4/4.
The Walls of Babylon, 1:43 - Another awesome groove. I wish they would've repeated it just once more at some point, though.
The Walls of Babylon, 2:32 - Great guitar/bass unison, and the drum groove is great.
The Walls of Babylon, 3:09 - Whenever Symphony X has a bass/drum only groove, it is bound to be great.
Seven, 5:04 - A very bare-bones guitar/bass part, but a great groove. Reminds me of the verses from "Incantations of the Apprentice," but better.
Revelation, 0:21 - Main groove that kicks ass, whether it's in F#m or Ebm (at the last chorus). The lead guitar line makes it better.
Revelation, 5:26 - This Fm groove and its under-solo variations in Abm and Cm are just old-school riffage at its finest.