Ayreon: Into The Electric Castle - this was the first Ayreon album I got into, and one of the first progressive rock/metal albums that drew me into the genre. I could actually list the entire saga as my favorite, but this was the album that started it all for me.
Symphony X: V - my favorite Symphony X album to date, this one has it all for me. While I really liked the material on the album, it was Egypt that grabbed me and wouldn't let go. The harmonic pre-chorus sung "in the round" is just haunting!
Fates Warning: APSOG - I picked up this album with no real idea what the story was about. As I listened to it, I formed a story about a man looking back across the years where he had a strong relationship with a woman. I was rather surprised to find out it was about the band's relationship with it's fans!
Dream Theater: Scenes From A Memory - as Metropolis Pt 1 became my favorite DT song, I was seriously hyped about this release. It lived up to my expectations and then some! I was even more surprised to here a riff from ITEC used in one of the songs here. Of the epic songs and concept pieces they've recorded since this, Scenes still remains my favorite. Unless they decide to release the 12 Step Suite as an official album. Maybe an EP?
Queensryche: Operation Mindcrime - while I'm not a huge Queensryche fan, this album does hold a special place for me. I realized one day that it was the first progressive metal and the first concept album I owned as a kid. You never forget your first time.
Definitely a great album, and sadly one of the last Queensryche albums I would fully enjoy. Empire would be the last.
Ever-FUCKING-grey: In Search Of Truth - it wasn't long after I joined the Perpetual Motion community that this came out, and I bit into the hype big time! I was blown away the first time I listened to The Masterplan, and this still remains my favorite Evergrey album. The Inner Circle is a very close second, and would probably be here instead of In Search Of Truth had it come out first.
Kamelot: Epica/The Black Halo - it took a while for me to get into Epica, but Black Halo grabbed me from the beginning. I'm a Kahn fanboy, and these albums really show why. Thomas' writing on these albums was stellar, and Ghost Opera and Poetry For The Poisoned benefitted from it.