[Yesspaz]

If you like experimental stuff, Godspeed You Black Emperor! does some long stuff, in the 15 to 30 minute range.

Focus has some long stuff.

Mogwai has an EP that's a 20 minute instrumetal called "My Father My King"

King Black Acid is a good try for "mind-altering neo-psych jams" as one reviewer put it. Heck, their fourth album is even called "King Black Acid Loves a Long Song."

And Tarentel is quite good at the extended neo-Kraut type stuff.

Speaking of which, try Autobahn by Kraftwerk.

Finally, never overlook Mike Oldfield. I've noticed that you name a lot of very famous proggers. Surprised Oldfield is not one of them. Go to the requests and try out Tubular Bells, Tubular Bells III, Ommadawn, Incantations, Hergest Ridge, the Taurus cycle, Amarok, The Wind Chimes, and The Lake (There are others, Tubular Bells II is on AM in a chopped up form. There is also The Songs of Distant Earth, but it's not on AM).

In short, LOTS of long prog songs on AM. Everything listed above is on AM for you to sample, with the exception if the Mogwai. Enjoy.