Ok, I must admit I haven't read through the whole of this thread but seeing the post about Tortoise as recommended by Douglas, it just so took me back to the days of Soft Machine. I was a young idiot at the time but this band really got me into the jazz rock fusion thing.

Check this out.

http://www.youtube.com/watch?v=97qHPAFrHXk

And here is part 2 if you're up to it!

http://www.youtube.com/watch?v=4L7n-bHwQ0s

I just had to search through my seldomly played CD's and I found the double album "Strange Fruit" which must be worth a bloody fortune by now!