Instruments in progressive rock

[Wojtek]

One of the most important reasons I am listening to progressive rock is that in this kind of music we can often hear very wide instruments kit. It's great to mix traditional rock "foursome" guitar/bass/perc/keys with other instruments, sometimes ethnic, sometimes less exotic but still intriguing.
I'd like to ask you about your favourite "non-rock" instruments present in prog. Flutes, saxes or maybe harpsichord and church organ, oboe or clarinet (these are of course examples)? Please justify your choice - is it because you love given instrumentalist's performance so much or because you're simply never fed up with sound of the instrument and feelings it evokes.
Finally, what are in your opinion unforgettable tracks/albums with unforgettable "non-rock" instruments' performances?