Spruce - here's some suggestions from me
Zoltabrane - I think this self-titled EP is still available on amazon, though their website has vanished. Indie instrumental progrock group from the US, really stylish retro stuff.
Steve Unruh -
www.steveunruh.com. This guy is one of the most innovative songwriters I've heard, and all his work is also independent. If you've ever heard Neal Morse or NDV's solo albums, he's a lot like them - very very clever lyrics and music. Generally pretty soft progrock. I recommend Beginning of a New Day, and Out of the Ashes.
(and if you haven't heard any Morse or NDV, I'll suggest them too. I have Neal Morse's self-titled solo album and NDV - Karma).
Arabesque - The Union. Dutch progmetal with dual female vocalists. Very impressive.
Porcupine Tree - In Absentia. I'm not familiar with much PT, but seeing as you're looking for them, I do have IA and it's great - really psyche in parts, definitely cool. And Steven Wilson has a sexy voice.
Spock's Beard - get either V or Snow. Snow is one of those albums where you never stop finding new things in it with subsequent listens.
Time Requiem - this is an insanely wanky keyboard progmetal project from Richard Andersson
Extremely nifty and worth a look.
Stramonio - this group has two albums, I can't remember what the first one is called, but the second one is Mother Invention. They're really different; the first one (which I've heard but don't own) is pretty good progrock, but Mother Invention is really oddball - lots of jazz thrown into the mix, and it's got some of the strangest lyrics ever. I really got into it.
In Extremo - German heavy metal with bagpipes in. Nuff said.
Paul Nelson -
www.paulnelson.com. His instrumental guitar solo album LOOK is very cool.
Rush - I agree with the 2112 vote - this has to be a definite
This was my first Rush album and well worth it.
Vanden Plas - you may already have their stuff, they're pretty well known, but I've never heard you mention it so I'll put in a word for them anyway. Awesome progmetal. Get Colour Temple or Beyond Daylight.
Karmakanic - Entering the Spectra. This is a pretty off-the-wall side project, a concept album, which features some of the Flower Kings.
Threshold - awesome Pommy progmetal - go the recent stuff for preference, Critical Mass or Hypothetical.
Devin Townsend - I just picked up Accelerated Evolution the other day and it's really grabbed me. There's something about his work which I really love, I can't totally put a finger on it yet, but this is a great album. Totally nothing like SYL though, of course.
It's a long list, take from it what you will
Remasters of their earlier albums are out now, bought Beware of Darkness yesterday but haven't listened to it yet.
